I have some conflicting thoughts here.
On the one hand, I don't think GW cares about the competition.
On the other, the popularity of competing kits in the realms of vehicles and generic units could mean they're hesitant to tackle vehicles. Plus it might not align with their plans for the game.
I don't follow GW closely, but I hear 10th greatly reduced the role of vehicles in the game. Especially when it comes to smaller games like Combat Patrol. if it's true they're making 30k a game with regular rules updates and new edition every 3 years despite the success of 30k being in part because it avoids the constant rules churn and meta chasing of GWs other games, then I can see them trying to push Spearhead (or was it Vanguard) model of seasonal army boxes where you "have to" rebuy your army every 3 months. And vehicles don't play well with that.
The boyz kit failed because GW was dumb and didn't include enough weapons for the loadouts, and it was rejected so quickly that they brought back the previous sprue.
As far as vehicles and GW selling them, HH is practically the tank game after 2.0 due to the number of vehicle releases for the thing. GW has show they'll still sell large kits for 40k with no problem whatsoever(necron silent king, void dragon, monolith. space marine dreads, the primaris vehicles, etc.). Generally speaking the vehicles even as older kits tend to look better by comparison than older infantry, but have you tried assembling a land raider or rhino recently? Or taken a look at the eldar falcon/wave serpent sprue? Then compare those to the modern kits, it's night and day. Sure, assembled they can look fine(with a lot of work) but HH has shown they can sell vehicles without issue.
As far as combat patrol, when it was 500 points vehicles never made much sense to begin with(lets not pretend there was any sort of balance), and now with combat patrols being closer to 350 points they make even less sense. Vanguard was just the aos name for combat patrol boxes, and it got changed to the spearhead boxes. That's not the seasonal aspect. The seasonal bit is the "spearhead gaming pack" for aos, which has the cards(40k already has annual mission cards, and before that it was the overpriced bullshit grand tournament books), some terrain, and basically a disposable play mat for $65. The seasonal bit for 40k is Kill Team, which GW has been using as an excuse to introduce new units for "big 40k" anyway and would have been comparable to Warcry(which was popular, other than the giant $200 boxes every 6 months, and I have no idea why they seem to have abandoned that).
If I were to point to something GW seems to want to abandon for 40k, it would specifically be aircraft as no matter what they've tried since 5th edition they're always in some quantum state of being overpowered or not even close to being worth their points(there was an ork list in 9th that used a bunch of aircraft and tabled an opponent in a tournament in round 1, and some harlequin lists at the same time spamming transports, that's what got GW to cap the number of aircraft and require transports to start loaded with something).
GW even continues to try and push the stupid 3,000 point "onslaught" game size for 40k, that no one plays and even their latest '25-'26 mission deck includes rules for 1,000 point games but the only major restriction is only being able to take 1 titanic character(big knight), and a couple months back introduced combat patrols for IK and CK.
Back to the point, once they're done with infantry and eliminating the last of the finecast, they'll be able to move onto a vehicle refresh at some point and it wouldn't be unreasonable for them to do so with 20+ year old kits. People take vehicles all the time still in 10th, just not parking lots of them unless they're guard.
