Mo’ Mobs and the old pistons mod? Yeah, they were, but that was wayyyy back then before Minecraft was worth literal tens of billions of dollars and became the single most popular game of all time; developing content for a game like that on its myriads of platforms and audiences and whatnot is hard. Really hard. I’m not saying that “modders have it easy”, making content takes time and effort, but it is a fundamentally different amount and kind when it comes down to making updates.
Addendum: Just for clarity, I’m not saying Mojang’s updates are perfect or great or anything really, I’m just saying that to make $x content for a Minecraft update and a Minecraft mod are 2 very different things.