in my unsolicited opinion its as simple as the pressure got to him eventually. cause he is a member on this forum, he reads everything on here (or at least used to). and there is only that much nagging about the updates and this & that one can take before before you start questioning will the update be good enough, is this the direction it should take, will people be pleased etc.
who knows, maybe he's just doing it out of spite at this point or whatever. at least to me its clear that we're not waiting for him to actually finish the update, but for him to be at a point again where he actually wants to release the update. i'm sure there already was an update ready to be shipped 2+ years ago, but he just wasn't happy with it.
like i said, just my pov.
edit: this forum is likely not his only source of feedback, but i'm sure his other feedback sources (like patreon etc.) show a similar general attitude towards it.