This is list reeks of entitlement.
> If it's a "seller's market", why do so many developers work under onerous IP contracts that grant their employers rights to what they build in their spare time?
Most developers don't have any IP to lose. If you have IP to lose then you can find a company that won't ask you to sign onerous contracts.
> If it's a "seller's market", why do so many developers work in noisy bullpen environments where they have to blast music into their ears with headphones to focus their attention on what they're building?
This is entitlement. Open office saves money. The only option that saves you from wearing headphones is a private office per programmer, which is rare (I think Microsoft still does this). The next common options is cubicles but you still need to wear headphones.
> If it's a "seller's market", why do so many developers have stories about working late at night and on weekends to ship features on bogus accelerated schedules they had little hand in setting?
We are well paid to get our work done. Doctors, lawyers, investment bankers, accountants all work as much or even longer hours. Also bad managers create bad schedules and bad cultures, this is across fields.
> If it's a "seller's market", why do so many developers accept payment in the form of equity that has to be executed at great expense immediately after leaving the company, and offers no actual guarantee of return after making that investment?
"Great expense" is an exaggeration. Other career paths don't have equity. 80% of the companies I've worked at gave me worthless equity. It's the game that we play. The other 20% made me ~$500k.
> If it's a "seller's market", why are developers forced to move to the most expensive real estate markets in the country to work every day from a particular office when their work can be done more productively from their own home offices?
No one is forced to move anywhere. People want to move here, still.
> If it's a "seller's market", why are so many developers compensated with equity whose terms they're not even allowed to fully understand? And why is it that their common shares are last in line after liquidation preferences and VCs take their rake?
"Not even allowed to understand"? That's a lie. If you work for a shitty company that isn't transparent, you can leave and work for another company that is. That's a seller's market.
Tech workers are generally much happier than other professions. Until that changes, you will never get unions. I hope it never happens, and I will never join a union, and I personally don't know a single programmer that wants to as well. Those that want unions are in the vast minority, and are much louder on forums like Hacker News, but it won't get much traction unless there's another dotcom bust.