We just had had a thread about the new v4 Alpha 4 [1], in which several people reacted incredulously [2][3][4] at why developers would feel pressured to upgrade from v3 to v4 for existing projects.
This news, not even 24 hours later, confirms others' and my fears [5], that v4's arrival will mean the cessation of releases -- including bugfix and maintenance releases -- on the v3 line, effectively making it abandoned.
Nothing stopping you or anyone else from keeping it up to date. I think it's silly to have these expectations from people creating free software for the world.
While I don't entirely disagree with your premise, this oft-repeated argument misses some key points.
Every user is free to make changes themselves but upstreaming them to the 'official' repo won't work, because the devs have decided they've moved on. Everyone is free to maintain a publicly-accessible fork, but without community coordination, the forks will diverge, unless widespread community consensus is reached about which one is the preferred survivor repo. Essentially, to solve the problem, merely dumping code isn't sufficient; you must also build a community.
Hence when a project's leadership decides they will no longer release/maintain/fix/accept-pull-requests-for a particular version, all of us lose the single most logical place where collaboration about that particular version happens. This is what I lament, not that woe-be-unto-me, I-have-to-fix-it-myself.