The unique aesthetic styles of these "kiddified" (stylised) series kinda makes them "incompatible" (for want of a better word) with other Transformers series. You can't really play with your Animated toys with figures from other series -- it looks weird. Same with Prime and RiD (which is odd because they're meant to be part of the same continuity and even putting these toys next to each other looks strange).

It also kinda takes away the "robots in disguise" magic because they look like they belong in a cartoon rather than the real world. One cool thing about a lot of TFs from previous series is that they look like they could be living among us. You get a Bumblebee that looks like a VW Beetle then you see a yellow VW Beetle in real life and suddenly you imagine that it could be a robot. Even many of the unlicensed vehicle modes look like they could be real vehicles. But the more stylised alt modes become the less convincing they feel as being part of our world.

And yeah, it also means that it's harder to blend these toys with other series.
e.g. TFP Knockout appears in the IDW comics as a Carcerian, but his stylisation makes him kinda stick out like a sore thumb compared to other Transformers, even other Carcerians (although you could very well make the same argument about Obsidian and Fat Tankor, and indeed the odd stylisation was a big bone of contention with Beast Machines). I absolutely love Animated Blurr - he's my favourite Blurr toy. But his highly stylised cartoon aesthetic means that I can't really mix him in with my CHUG toys because he just sticks out too badly. Or take Animated Arcee vs Generations Arcee -- Animated Arcee is arguably a better designed toy being not a shellformer, but she just doesn't blend with CHUG's G1 aesthetic. Generations Arcee on the other hand blends so well that you could put her next to your G1 toys and she'd look like she belongs. Same with POTP Slash. In fact, I posted comparative group shots of my G1 and CHUG Dinobots on another forum, and in my G1 group shot I snuck in Slash and didn't say anything. Nobody picked me up on it. She blends in that well!

And aesthetics aside, these are really just badly, badly designed toys. Even if they were based directly on their G1 designs they would still be rubbish.