Google doesn't always update when the new ramp goes into effect and can sometimes lag by a few weeks or more from what I've personally experienced, living around places experiencing rapid redevelopment.
Sounds like someone who's never in their life driven in Austin.
It wouldn't surprise me to find it's nearly a half dozen per year, on a slow year. I only drive down there a few times a year and yet almost every time I go on my random route at least two stretches of road are just radically different from the last time I drove on it.
Sometimes it really feels like Texas' biggest industry is highway bridge/overpass construction.
If you've never experienced the rapid redevelopment of Texas exurbs and what not it's something of a marvel to behold, like watching a train wreck take place over months.
Like did a bunch of teenagers sneak out at night and build a highway?
How hard can it be to have a process where mapping companies can register with a state’s DoT and get information when they build stuff?
With how some of this urban design happens it almost feels to be the case at times.
A bit more real of an answer is: federalism. You're assuming the state DoT is entirely in charge of these projects. Lots of different government organizations are in charge of these things, and they don't always communicate well. Cities, counties, toll operators, and others can decide when these ramps are opened or closed. It's not just the state DoT that does these things. There's no single org that can authoritatively say "these are all the roads which are open, right now."
Now, I do agree with you, making such a data set complete and public should be some level of priority. There should be reporting standards involved in defined, standardized formats. These do not really exist, and making such a thing happen is a political question not a technical one.