Two NLCS appearances with one of those being a 7 game closely contested series doesn't feel like enough data to claim a plateau to me. Two other playoff appearances fizzled out with cream of the crop All Star closers on the mound that blew late game, potential series clinching leads. So that's 4 playoff appearances, the other 3 included a sub .500 team in the shortened 2020 season that probably wouldn't have been a playoff team in a normal season and two sound first round defeats to teams that went on to appear in the World Series.
I don't necessarily disagree with those that have an opinion that they should spend some money to get over the hump but I'm not actually sure this would be the year to do that.
Also they've never really behaved that way. They've expanded their typical spending limits before and it didn't really pay off quite how they hoped, I think they're just committed to sticking to a plan at this point. There are just so many variables, your MVP candidate might hit a foul ball off his knee late in the season and be lost for the playoffs. Maybe one or two of your best guys goes cold at the plate for 4 or 5 games and you get swept.
It's difficult to predict and account for the small sample even when you throw a bit more money at the wall and hope. The Dodgers aren't just spending on one or two guys, they're buying 10+ of them. They had 13 players on their roster last season making 8 figure salaries, 7 of which were making $20M or more. The Brewers had 3 players with 8 figure salaries, Hoskins didn't make the playoff roster and Chourio made less money than all 13 of the Dodgers guys making 8 figures.