When taking into account the total amount of time involved in a traditional multi-round interview process (which can potentially go on for months depending on the company), the travel time required for any in-person interview rounds, and the time spent practicing leetcode drills in preparation for these interviews, 10 hours is nothing.

10 hours on some project per interview

Like interviews aren't lengthy enough as-is. I had an onsite the other week with two sys design, two leetcode-esque, a hiring manager, and a project manager.

I'd take that any day over the take home project I had to do in a subset of common LISP fresh out of college. Twas NOT a fun weekend, especially since I had no familiarity with LISP. With few exceptions, I don't do takehomes anymore. I don't want to spend an hour or so fuddling with your/your vendor's poorly documented, buggy environment (or setting it up myself) on my own time, outside of office hours, talking to exactly zero human beings during the actual process. It teaches me nothing about the company or team I'd be working on, doesn't allow for any gauge of culture fit, and (unlike leetcode) doesn't make me a better programmer.

That is one way to look at it I guess. But if it means a substantial pay raise then the amortized cost of those hours is negligible.

I see this complaint a lot, but 10 hours is crazy - I've been involved in setting, reviewing the results for, and doing such tests for many years and the longest I've ever expected anyone to take is 2 hours, which is more than enough to demonstrate whether you have at least basic capabilities as a programmer. As it is in the "real world" my biggest problem with other devs is for them to spend days on a story, then finally put up a PR that shows they really didn't understand the requirements well or make any attempt to clarify them. It's actually pretty rare I'd ever expect a dev to be able to take a story away and put anything like 10 hours time into without needing to discuss it first, so why would I expect that for a take home test?