I must echo aramis erak in that it strikes me that there is something abnormal about your table top RPG experience.
Yes, RPG's are sandbox ready out of the gate. If you set up the campaign world correctly the "improv" is not nearly as hard as you think.
I run a star wars game set during the original trilogy - I have no "plot". After the initial session, everything cues off of the players drives, and what they want to do as the crew of their ship.
Yes you do need a GM that knows how to set this type of campaign up. But It is not as hard as you make it out to be, and the information/advice on how to do it is readily available.
Just because you can spend hundreds of hours wandering around a video game, doesn't mean that it will still have constraints a RPG does not.
If all you've known from RPG's is pre-written modules, pre-plotted adventure after adventure, and railroads, it seems that you have really been missing out.
I'm well aware of the cutting edge of the videogame industry. Members of my group work in it. RPG's still do things no videogame can match.
Your gaming preferences seem to lie more in line with what videogames have to offer than your experience with RPG's. That's perfectly fine.
If the GM has to set up a campaign world, then the game isn't 'sandbox ready out of the box'. Yes, if a GM invests the time and trouble to work up hundreds of locations in advance, an RPG can be sandbox. But how often does that happen? I'm known for the extensive detail and long-term nature of the campaigns I run, (I've been GM'ing since 1979), but even I don't plug that level of effort into a campaign. The practice is that sooner or later the PCs encounter a plot hook.
Whereas Skyrim, to grab one game as an example, does literally come as a sandbox straight out of the box. Once you get past the avatar set-up, you can wander about pulling random encounters, random quests, home-building, Guild careers, life as a werewolf or vampire,
trade, trophy-gathering, crafting, and more for literally hundreds of hours. Before taking part in local politics and thinking about the core plotline.
And that's a game that's years old.
I've seen a lot of improv RPG campaigns, where unprepared GMs make stuff up off the top of their heads. If the players work with it, it can be OK. Every GM improvs and feeds of player speculation and drive; I do it literally every week. It's no substitute for preparation, but expectations vary from table to table.
But you've yet to point out what a CRPG
can't do. In this era of professional voice actors, multi-layered conversation trees, co-op, online play, ever-more-comlex processing speed, and the like, TTRPGs are seriously challenged. Few GMs can manage the sheer volume of detail that a CRPG can deliver.
TTRPGs currently have an edge, but it is a slender one; VTTs have given them a extension, because it helps deliver a higher level of detail. But take a look at this site: there's always threads discussing dealing with problem players, problem GMs, the difficulty in getting groups together. How many posts have you seen where a gamer mentions that they have Game X or Game Y but have never managed to run a campaign in it? I know I've made that very post more than once. This site is frequented by hardcore gamers, the sort who will stay with the hobby to the bitter end, but we aren't the majority.
CRPG quality grows constantly. TTRPGs have gotten VTTs, publisher support is still fairly steady, and the Net has made fan-based work easily available, but there's not a huge amount of change pending.