Maybe I've been unintentionally signalling that I'm capable of doing more and that's why I keep finding myself in this situation?
I'd be much happier if I had half the salary and somehow was able to work 2x12hr days instead of 5x8hr days, but I have no idea how to find employers that would agree with that. If you could get two people like me to do 2x12 at increased productivity during work hours with half the cost, you'd be coming out ahead, and you'd have more knowledge on tap in the organization.
In practice, it's fairly easy to keep all parties happy, though inevitably there will be stretches where one client really wants my time at the expense of my other projects. That's a fine line, but I haven't run into issues with it yet. I'm sure someday I'll over-commit myself and pay for it. Thus far the key has been responsiveness and "general availability", being open about when/how I can give them more focused attention for various projects. If I tell client A I have a big deadline coming up for client B or vice-versa, they're usually pretty understanding.
Best suggestion I could offer would be to talk to your friends/network and see if anyone "needs help here and there", to see if that opens a conversation towards an independent contractor arrangement.
If I had a clear goal of "get this done for the week" and that was it, why wouldn't I just do it as quickly as possible and then not do anything else? I just assumed this whole system of meetings/checkins/standups/code-reviews/slack-channels/etc was set up to avoid people doing that.
If anything, I feel more pressure to be readily available when I'm remote.
Being an independent contractor is awesome (it's what I did for 100% of my income from 2004 until just a couple of months ago) but the health insurance situation and fear ended up killing it.