Why animal mechas are so popular ?

Because animals are more dynamic than cars.

I've got a question regarding the ending of Dairanger (reading spoilered text at own risk!):

How did Clay Clone Shadam come to take the real one's place? What would have happened with the real one? Did he maybe reform the Gorma, hence their reappearance in 2044?

What's kind of mechas a musica-themed could have ?

A music themed Sentai sounds like it should have happened sooner now that you mention it, drums for legs, a triangle for the head, a guitar and cello for the arms, a flute sword (As a Zyuranger callback too) and a piano body?

The current Kyuranger ratings and toy sales are good ?

No, ratings aren't great (episode 6 or 7 was the lowest ever for Sentai, beating out a 20+ year record IIRC) the toy sales are projected to get to ToQger levels, but after two years of failures, I don't know if that's an acceptable end point. Though I guess anything in the way of an increase would be good.

Toei could not give less of a shit about ratings, it's all in the toys as that's the show's biggest money maker. Carranger had bad ratings too but it saved Sentai due to MASSIVE toy sales iirc

I never mentioned whether or not they cared, I was answering the guy's question.

But, yeah, they do sorta care. At least when they're doing very well. The Decade team was proud of the high ratings the series earned. They don't use them as much of a marker for failure, but high ratings are always a bonus for the people making the show.

Also, Carranger didn't save Sentai. That's a rumor that's been debunked for a while. Jetman was the series that saved Sentai, the cast was outright told that it would be the final season.