The issue is giving long term deals to any depth guys.
Here are the number of bottom six forwards signed to deals of at least 2.5M with at least 3 more years left on current playoff teams:
Pittsburgh - one (McGinn 2.75 x 3 left)
Carolina - zero
Rangers - one (Goodrow 3.6 x 5 left)
Washington - zero
Florida - zero
Tampa Bay - zero
Toronto - zero
Boston - zero (One if you count Coyle but he's supposed to be their 2C)
Colorado - zero
Minnesota - one (Greenway 3 x 3 and that's a 25 year old former first round pick who scored 32 in 56 last year)
St. Louis - hard to say because they run three lines but at the moment one - Saad 4.5 x 4 left but again this is a consistent 20 goal scorer with lots of top 6/pp time in his past and isn't a true depth guy
Nashville - one (Sissons 2.9 x 5 left)
Calgary - zero (Coleman is their 2nd line RW and 4th on the team in 5v5 TOI only behind their top line)
Vegas - zero
EDM - zero
LA - zero
Not a single team has multiple depth guys like that signed to reasonably pricy and long term deals. The Penguins, Rangers, and Predators are the only team with a true bottom six depth guy in that group.
So this isn't exactly fair. Just for an example, Carolina has Jordan Staal playing 3C and he was signed long term originally. Martinook is on a 3 year deal, just re-signed, also a 3rd liner.
Nashville signed Scissons long term who was not more than a 3rd liner originally. They also signed Jarnkrok way back when who's contract is just now expiring. He's a 3rd liner.
Washington signed Hagelin (4 years), Hathaway (4 years) and Eller (5 years), all are 3rd liners (at best in Hathaway's case).
Pittsburgh just signed McGinn to a 4 year deal and signed Tanev to a long term deal but lost him to Seattle.
Winnipeg signed Lowry and very well may sign Copp long term shortly.
Vegas, by their addition of Eichel, pushed Karlsson down to the 3rd line, he's signed long term. They also signed Stephenson (who has improved since signing his deal) to a 4 year deal. He was pretty much a 3rd liner when he was signed (26 points in 65 games and 11 points in 64 games the 2 seasons prior to that contract being signed).
Good teams recognize guys who can help fill roles and keep them a while. I'm not saying hand out 6 year deals to every 3rd liner but having a couple of foundational swiss-army knife guys signed to 4-5-6 year deals isn't going to hinder them. Especially considering the cap will increase in a couple of years and when it does, it will go up quickly, making these longer term deals more attractive in general