It's not weird, it's business. These IPs have generated millions of dollars and they're proven to work. A new adaptation means a new studio can milk it for dough, and generally they don't have to work nearly as hard because there's a pre-established fanbase.
Look at it this way, we all looked at the still of the series and immediately went
when we saw it. But it's TMNT, and people are gonna check it out because of that. Imagine if this studio made their own IP, we'd look at it and still go
but now nobody is gonna check for it because there's no installed fanbase.