The way you worded it sounds very negative, as if the only reason for keeping thing locked down is to extract maximum profit.

If you had said something like "fund the work" it would have sounded more acceptable. There is a large space between "extracting maximum profit" and "doing work for free".

What other reason is there for keeping something locked down?

Off the top of my head, scientific publishing. Keep it locked down until you have published then open source it.

I personally wouldn't want my work code online, as its always rushed and there is a fair bit of technical debt I would like to to refactor, rather than having potential employers thinking that I always write shit code. Feature requests are valued more than code quality.

I suppose wanting to hide perceived 'shoddy' workmanship is a reason.

I say, let it all hang out. Code can be continually improved.