Except they're not. Underneath the surface, Payback is effectively a very modified version of 2015. Same assets, same crappy garage system, same crappy menus, same crappy physics, etc. A few things from 2015 are broken or removed, and the amount of major changes can be counted on one hand.
Heat is looking to be very much of the same. The garage is very similar (only five cars shown at a time), the clunky menus are still there, the wrap editor still sucks, the "all-new handling model" is just a tweaked version of the one that we've been using since 2015, pursuits are still largely based off 2015/PB's system, the graphics are barely any different from 2015/Payback (although the art direction is definitely helping to make this game look unique), etc. These are all areas that I think need to be either be improved upon or redesigned completely, but won't because it's easy to just reuse stuff from the last couple games.
Yes, I'm aware that reusing assets is a normal phenomenon and that building a game from scratch is a very heavy undertaking, but 2015 isn't exactly the greatest base for them to be building off of.