Had to think about it for a moment, but I would say the fundamental problem with adding more content to Minecraft is this classic game design quote:

Given the opportunity, players will optimize the fun out of a game.

Source

In early days of Minecraft, you would cut down a tree, then slap down 6 blocks of wood and that was your table. It looked fine, because everything was just blocks and the few available blocks all could be combined without it looking terrible.

Now you've got a magnitude more blocks and the player looking to ruin their fun will spend far too much time:

• Choosing colors to combine. It can't just be wood, it's gotta be jungle wood, to make it fit in with the orange color highlights.
• Choosing block shapes. Can't just be a regular 1m³ block, it's gotta be an upside-down stair. And a carpet on top as a table cloth.
• Farming those resources. You need to find a jungle and a sheep. And scissors to collect the wool. And then you need to craft those stairs and carpets.
• Placing blocks. An upside-down stair can't just be slapped down. Instead, you need some scaffolding against which you can place it from the correct angle. Nope, not that angle. Gotta remove the stair and place it anew. And don't forget to remove your scaffolding afterwards. And place back those blocks you had to remove to get to the correct angle.

There are folks that find it relaxing to mine for hours and to spend hours getting every detail perfect about their build. But even those folks presumably wouldn't call it fun.

But of course, your community will still ask for ever more hyperspecific blocks to be added, so they can optimize the fun out even more. Because your community are not game designers.