Microsoft painted themselves into a corner with Windows and backwards compatibility.
They do crap like UI mixing (old and new versions existing together) because backwards compatibility is what got them the marketshare they have in the enterprise (well that and anti-competitive practices). At some point, to improve their products, they are going to have to break compatibility and just push forward, and yet they can't because that would immediately alienate a significant portion of their enterprise customers that rely on that compatibility to run old software from vendors that no longer exist, that are critical to operating some niche equipment - hell, it's not uncommon for me to see air gapped windows XP machines still in production running some critical workload.
So they're stuck because they both simultaneously need to move forward but also can't break the old stuff without screwing over their customers.
They do crap like UI mixing (old and new versions existing together) because backwards compatibility is what got them the marketshare they have in the enterprise (well that and anti-competitive practices). At some point, to improve their products, they are going to have to break compatibility and just push forward, and yet they can't because that would immediately alienate a significant portion of their enterprise customers that rely on that compatibility to run old software from vendors that no longer exist, that are critical to operating some niche equipment - hell, it's not uncommon for me to see air gapped windows XP machines still in production running some critical workload.
So they're stuck because they both simultaneously need to move forward but also can't break the old stuff without screwing over their customers.