But they point the comment above is making is that the years of support add a bunch of features that wouldn’t exist otherwise. Sure, they could just not. Why would they do that though if they have a team who knows how to work on a thing and people willing to pay for it.
For example, BG3 exists because the studio continued to make games in the same style in the same engine for a very long time. They became absolute experts in it, and continuously improved their tools and techniques. You don’t get that by constantly making new different games.