Before 5E, I'd been on hiatus since the waning days of 2nd edition. Quit around the Skills and Powers era because I didn't like the direction TSR was taking their books. Dabbled with GURPS in the meantime, played a couple of 3E computer games, played some Shadowrun, but for all intents and purposes, until I tried 5E I hadn't played any (A)D&D since 1997ish. Obviously they did a good job from my perspective, good enough to reel me back in.
There are things I like about GURPS (especially the GULLIVER ruleset), but the thing that attracts me to D&D is twofold: classes and levels, and powerful magic (Fireball!). I've tried building those things into GURPS but it never really worked out right.
The thing I like about classes and levels is that it constrains your choices. In a completely point-buy system, it's too easy to optimize. You can make a 50-point GURPS character (think 0th level) who can practically destroy the world if you let her spend points freely; in practice the suggestion is that the GM constrain how you're allowed to spend your points, charging Unusual Background costs for weird abilities... what happens in practice is by the time you create formal structures for how point-spending is allowed, you've recreated the idea of classes, poorly. To put it in computer science terms, 0/1 knapsack problem is more interesting than the unbounded knapsack.
Practical example: look at 5E wizard specialties. Not all specialties are created equal, and if I could freely choose abilities from any specialty, I'd probably take Portent at level 2, Undead Thralls at level 6, Focused Concentration at level 10, and Illusory Reality at 14th. Not only is that kind of incoherent from a roleplaying standpoint, but I didn't have to make any agonizing decisions! If I pick Portent in 5E by RAW, I have to be a Diviner, which means I can't get Undead Thralls, but I could focus primarily on being a Battlemaster fighter and just use Diviner 3 for some extra defense and a familiar and Portent, etc. Not only do class limitations (vs. point-buy) enforce flavor, they also make chargen more constrained and therefore a more interesting optimization problem. Point-buy systems don't, so that's one draw of D&D.
I don't think I need to say anything about magic and Fireball. D&D has strong and interesting magic, and GURPS does not, and that's that. (My experience with Shadowrun probably made it easier for me to accept the 5E concentration mechanic though.)