The basic reason is what I've discussed before - Messier, like Lemieux, was better equipped than Gretzky to deal with better defense, tougher opposition.
Dude, you need to give this up. It's becoming like your life's mission to discredit the greatest forward of all time.
When I think about the Oilers scoring big goals, I think first of Messier and Anderson, not Gretzky and Kurri. I think anybody who watched the Oulers would say the same.
Forgive the essay, but I have to do this.... The following are all playoff games that the Oilers won during the 1980s and with Gretzky, Messier, and Kurri all as teammates:
1981 vs Montreal:
Game 1
Kurri 2 goals (both assisted by Gretzky who had 5 points)
Messier 0 points
Game 2
Kurri 1 goal (third period clincher)
Messier 0 points
Game 3
Gretzky 3 goals (4 points) to clinch series win
Messier 0 points
1981 vs. Islanders
Game 3 (Oilers already down 0-2 in series)
Gretzky 3 goals, Kurri 1 goal
Messier 1 secondary assist
1982 vs. Kings
Game 2 (Oilers down 0-1 in series)
Kurri 1 goal (late in third to send it to overtime)
Gretzky 1 goal (overtime winner)
Messier 0 points (and minus 2 on 2 Kings' goals)
Game 4 (Oilers down 1-2 in series after blowing 5-0 lead in game three)
Kurri 1 goal (ties game in first period; Oilers go on to win)
Messier 0 points
1983 vs. Winnipeg
Game 1
Gretzky 4 goals, 5 points
Messier 1 assist
1983 vs. Calgary
Game 2
Kurri 1 goal (opens scoring in 1st minute)
Messier 1 secondary assist (on meaningless late third goal)
Game 3
Gretzky 4 goals, 3 assists
Messier 3 goals (two with primary assist to Gretzky)
Game 5 (Oilers clinch series)
Gretzky 1 goal (3 points)
Messier 1 goal
1983 vs. Chicago
Game 1
Gretzky 1 goal (5 points)
Messier 1 goal (3 points)
Game 4 (series clincher)
Gretzky 1 goal
Kurri 1 goal
Messier didn't play
1984 vs. Winnipeg
Game 1
Gretzky 1 goal
Messier 0 goals
Game 4 (series clincher)
Kurri 1 goal
Messier 1 goal
1984 vs. Minnesota
Game 1
Gretzky 1 goal
Kurri 2 goals (both primary assists to Gretzky)
Messier 0 goals
Game 3
Gretzky 2 goals (second of game and penalty-shot closer)
Kurri 1 goal
Messier 1 goal
1984 vs. NY Islanders
Game 4
Gretzky 2 goals (incl. opener)
Messier 1 goal
Game 5 (Cup clincher)
Gretzky 2 goals
Kurri 1 goal
Messier 0 goals
1985 vs. Kings
Game 1
Kurri 1 goal (series opener)
Messier 0 points
1985 vs. Jets
Game 1
Kurri 1 goal (and Gretzky EN goal)
Messier 0 goals
Game 2
Gretzky 1 goal (opener)
Messier 1 goal (scores late in third when game already over)
Game 3
Gretzky 1 goal (game winner, late in third)
Messier 0 goals
Game 4 (series clincher)
Gretzky 3 goals (and 4 assists)
Kurri 3 goals (and 1 assist)
Mesier 1 goal (in third period when game was already over)
1985 vs. Chicago
Game 1
Gretzky 1 goal
Kurri 2 goals
Messier 0 goals
Game 2
Kurri 3 goals (2 on Gretzky primary assists)
Messier 0 goals
Game 5
Gretzky 2 goals
Kurri 3 goals
Messier 1 goal
Game 6 (series clincher)
Kurri 4 goals (all 4 with primary assists to Gretzky)
Messier 2 goals
1985 vs. Philadelphia
Game 2
Gretzky 1 goal (Oilers only score 2 legit goals)
Messier 0 points
Game 3
Gretzky 3 goals (and 1 assist)
Messier 1 assist (on a Gretzky goal)
Game 4
Gretzky 2 goals
Messier 1 assist
1986 vs. Vancouver
Game 1
Gretzky 1 goal
Messier 0 goals
Game 2
Gretzky 1 goal
Kurri 1 goal
Messier 1 goal
Game 3 (series clincher)
Gretzky 1 goal
Messier 1 goal
1986 vs. Calgary
Game 4
Gretzky 3 goals (and 2 assists)
Messier 1 assist
(This is the only series the Oilers lost from 1984 to 1988. Gretzky scored 5 goals and Messier 2.)
1987 vs. Kings
Game 2
Kurri 4 goals (all with Gretzky assists)
Messier 2 goals
Gretzky 1 goal
Game 3
Kurri 2 goals
Messier 2 goals
Game 4
Kurri 1 goal (and Gretzky 5 points)
Messier 1 assist
1987 vs. Winnipeg
Game 3
Kurri 2 goals
Messier 1 goal
Game 4 (series clincher)
Gretzky 1 goal
Messier 0 goals
1987 vs. Philadelphia
Game 1
Gretzky 1 goal (opens scoring)
Kurri 1 goal
Messier 0 goals
Game 2
Gretzky 1 goal (opens scoring)
Kurri 1 goal (overtime winner... largely set up by Gretzky)
Messier 0 goals
Game 4
Kurri 1 goal (and Gretzky 3 assists)
Messier 0 goals
Game 7 (Cup clincher)
Kurri 1 goal (Cup winning goal)
Messier 1 goal (opener for Edm.)
1988 vs. Winnipeg
Game 1
Kurri 1 goal
Messier 1 goal
Game 4
Kurri 2 goals (both assisted by Gretzky)
Messier 0 goals
Game 5
Gretzky 1 goal
Kurri 2 goals
Messier 2 goals
1988 vs. Calgary
Game 1
Kurri 1 goal (game winner)
Gretzky 1 goal (clincher)
Messier 1 goal (opener)
Game 2
Gretzky 2 goals (incl. overtime winner)
Kurri 1 goal (game tier)
Messier 1 goal (pass bounced off Flames' D and went in on the PP)
Game 3
Kurri 1 goal (third period clincher)
Messier 0 goals
Game 4
Gretzky 1 goal
Messier 1 goal
1988 vs. Detroit
Game 1
Kurri 1 goal (and Gretzky 3 points)
Messier 0 goals
Game 4
Kurri 2 goals (incl. overtime winner)
Messier 0 goals
Game 5 (series clincher)
Gretzky (EN goal)
Kurri 1 goal
Messier 1 goal
1988 vs. Boston
Game 1
Gretzky 1 goal (series opener)
Messier 0 goals
Game 2
Kurri EN goal
Gretzky 1 goal (game winner in third)
Messier 1 goal
Game 4 (or is it 5?) (Cup clinching game)
Gretzky 1 goal (Cup winning goal)
Messier 0 goals
___________________________
So, I guess you just forgot about those specific games, eh?