The compilation step is a major pain. Even after using it for several months straight, I feel like I'm in a constant battle with the compiler. It's slow and difficult/annoying configuration problems keep coming up from time to time. It slows down my debug cycle and the compilation delay makes me lose my train of thought. I used to love using console.log() to quickly test an assumption in JavaScript; you cannot do this with TypeScript (it's not practical given the 5 to 20 seconds compile time); you have to use the debugger every time and step through stuff (even when you have a very good idea about which specific variable you want to check) - It's extremely cumbersome.
I have gone back and forth from dynamically typed languages to statically typed languages many times for years and I've spoken with engineers who used to be Java developers for many years, then switched to Javascript, then TypeScript and they shared the same thoughts as I did. TypeScript is slow and restrictive in a way that is unnecessary. It's got Microsoft all over it.
Also it forces all developers to use bulky commercial IDEs like WebStorm because you rely more on code completion to help you figure out the right types. You can say goodbye to Atom, Sublime and the rest... Atom's TypeScript plugin is not good enough unfortunately.
At my previous work, even developers who said that they liked TypeScript secretly didn't like it because they used the 'any' type Everywhere.
I wonder if the people who are making this decision have actually tried TypeScript themselves for any decent amount of time on a decent sized project. I don't think they know what they're getting into.
I decided not to renew a lucrative contract at a finance firm as a front-end developer in part because I did not enjoy using TypeScript every day.