Oh, come on now. Just a pebble from the street at the miserly rich man's house....
Seriously, they've been like the old phone company. Like Lily Tomlin's Josephine the Operator used to say, "We're THE PHONE COMPANY, we don't have to care." As the dominant os on the planet, they (Bill) didn't feel any need to write anything new. Just keep building add-ons.
They never fix anything until they have to, and they don't seem willing to develop code that doesn't build on the known faulty foundation. It can be done, witness the pressure Linux is starting to put on them.
I know how to build an home environmental system that won't cost and arm and leg to run and out-performs 90% of what's out there, and I do it every time. Won't take the easy path for the quicker buck. Every time I learn a better way to do something, I use it. I have completely changed the entire method of design and install radically from where I started 25 years ago. The basic physics didn't change, I did.
Bill has learned, and knowledge is greater now, but its been cheaper so far to just keep on doing what he has been doing with 'more and better' added each time. A programmable T-stat does not a modern system make...