Why there's no modern clone of Desktop Tower Defense?

It's a pivot, but check out the indie game Exodus Borealis on Steam. The tower defense part of the game lines up with some of the Desktop Tower Defense features. The enemies path to the goal (your town) is entirely in your control by clever placement of walls, and a variety of tower types.

The other part of the game is a small city builder. You're overseeing a colony of washed-ashore survivors trying to make a new life on a (cursed) island. You need to maintain a stable population to mine resources, and build your tower defense maze.

https://store.steampowered.com/app/1528810/Exodus_Borealis/ Made by a former colleague of mine.

That was a great game. I tried to find a new TD game a few years ago and like you found it difficult to find any good ones.

I did find an iOS TD by carrot (cairrot?) games - they seemed Chinese, and that was VERY good. I don’t think the planned sequel ever came out. Would be interested to hear about who they were and what happened to them.

Not answering what you're asking, but: there used to be many many many Tower Defense custom maps for Warcraft III: Reign of Chaos. I don't know if pure-original-non-remastered-RoC is still buyable or installable, but that could scratch your itch.

I never played the original version but I certainly played many derivatives.

There’s probably a good clone of it, but it’s lost in all of the copy cars. What’s the everyone’s favourite version (would love one for iOS)?

I loved it as well, the OG flash version. That and Gemcraft. I have a concept for a 3D Tower Defense I'd like to do in ThreeJS, where the enemies approach in log spirals ;)

DTD is the only game that ever made me stay up hours past my bedtime. So awesome.