I can sort of understand the publishing argument, since npm doesn't solve for this at all, unlike JSR:

"You publish TypeScript source, and JSR handles generating API docs, .d.ts files, and transpiling your code for cross-runtime compatibility."

Not allowing it for private modules doesn't make much sense to me, though. It either forces me to use a loader, or now figure out a JS build step which I have been more than happy to avoid up until now.

The implication is that the capability is implemented to conditionally allow, which I suspect has been deliberately avoided, less because the change would require much technical effort (though it might; I don't know) than because the PR to make it offers another opportunity to keep that door nailed firmly shut.

As a past and present module author, I don't feel myself unduly burdened by the need to maintain the tooling to support the work I publish. Or present-ish, anyway; last time around it was Bower and about Node 8, and the experience these days is worlds more comfortable.

I can see why others would feel differently, but again, I'm not really here to argue preferences. If you'd like to fill your afternoon instead with an enjoyable, on-theme read, try the UNIX-HATERS Handbook: https://web.mit.edu/~simsong/www/ugh.pdf