Too be fair the most successful years on there, the league only had 6 teams so its understandable they'd win and compete for more Cups
Unfortunately, that was never the case, and the Bruins NEVER won the Cup in a six-team league. In 1929, there were ten teams, and in 1939 and 1941, there were seven.
The odds were never stacked more against the Bruins than in the O6 era (1942-1967). In the Original Six Era, Montreal (10), Toronto (9), and Detroit (5) won all the titles except for 1961 when the Blackhawks (1) somehow snuck in.
Back then, there was no draft, and each team had exclusive rights to any player who lived within 50 miles of the home rink. Needless to say, Toronto and Montreal benefited greatly from this. With a handful of exceptions, Montreal had a stranglehold on the province of Quebec, and Toronto had a vast network of scouts and talent-finders throughout the rest of Canada who signed promising young players to iron-clad contracts. Detroit’s proximity to southern Ontario helped them. The Red Wings found Gordie Howe in Saskatchewan, but the Bruins, Rangers, and Blackhawks struggled mightily to get great players in the O6 era.
Stan Fischler’s history of the Bruins in “Bobby Orr and the Big Bad Bruins” recalls that the Bruins were so desperate for a savior in the early 1960s, that all the scouts and managers formed what he called the “Bear Expeditionary Force” to find the next great Bruin. They looked all over Canada, and eventually got their man. But the only reason they did was because Bobby Orr was 12, and the Maple Leafs in their arrogance considered him too young to sign. The Leafs did not take into account how desperate the Bruins were and thus botched what should have been a layup in signing Orr who was a huge Maple Leafs fan.
Other great Bruins like Eddie Shore and the Kraut Line were from well outside the territories of other NHL teams. Though Shore was bought from a defunct league, had he been born in Ontario, he undoubtedly would have been a Leaf.
The Original Six was not the utopian hockey paradise some like to pretend it was. Unless you were a Habs or a Leafs fan, it sucked much more often than not. Especially when the best Boston, New York, and Chicago could hope for was the fourth playoff spot after Montreal, Toronto, and Detroit settled the order they would finish 1-2-3.