1.7.10 is dead only because Forge devs are dropped support for Forge for 1.7.10. If somebody is going to find a bug in this version (like messed up AABB), nobody is going to fix that, and the only solution would be is to host your own version of Forge.

I do agree, however, it's not laziness that keeps big mods stuck at 1.7.10, but stupid changes to the API. Those changes add a lot of work to modders, but on other hand, JSON models are great or Capabilities system. JSON models allow people to create fancy models for blocks in texture packs or even cool item models like those rad katana swords, while capabilities allow more flexible way of storing mod's data while also allowing to create your APIs.

What other things are great about newer versions are that they're still supported by ForgeCrafters, much more hooks, and more. The problem with 1.7.10 modders with newer versions, is the need to relearn stuff, which can be quite hard. Other than that, I think new versions are great some of my mods weren't be possible without new features. That's my opinion, anyways