My instinct is that this is partly due to how hard it was to get upgrades as a user. Devs would have taken the release cycle very seriously when people couldn't

My instinct is that this is partly due to how hard it was to get upgrades as a user. Devs would have taken the release cycle very seriously when people couldn't just get the next microversion pushed to them. I remember bringing home updates on 3.5in floppies, or having to download them on slow dialup connections, all very much about pull not push.