That's not true - the option of boycott is always available, and a concerted and sustained effort would have certainly made GW reconsider its stance. Nevertheless, I have no doubt that GW had carefully considered and evaluated the likelihood of it before terminating the line.
AoS wasn't announced a year in advance with preorders or anything. There wasn't anything to be boycotting. WHFB already weren't buying product. Once AoS launched, GW wasn't going to reverse course and immediately bring back WHFB. AoS brought in a massive influx of new players, with a lot of the older ones initially not bothering for the first year or so till the generals handbook came out due shit like not having points, abilities based on people yelling the loudest and other dumb crap(nagash's stupid hand of dust thing is still in the game for 4.0... fucking ridiculous).
The reality is that GW has a near-uncontested foothold in their industry, and 3D printing is not simple enough for casual players to adopt nor was it back then. That and with the fanbase being completely pliable as it is, they would have to relaunch 40K with the Space Marines as Pride Parade Pronoun Marines for any real damage to occur. Since relaunching Space Marines as Primaris, terminating WHFB and continuous price hikes hasn't done much, I'm sure this latest kerfuffle is barely an issue for them.
The part about 3d printing is absolutely true. It is its own hobby and mess that most people simply don't have the time for, regardless of how many "maker" youtube channels might try to have people believe otherwise. I have a resin and FDM printer, hate using both of the damned things for a variety of reasons. We're still years off from truly plug and play 3d printing. As far as relaunching models and price hikes not doing much, I'd say their stock value shows the opposite as the skyrocket began even before covid.
There was nothing stopping GW from doing more with WHFB besides nuking it from orbit, mind you. The stagnation was entirely due to them.
There was also nothing stopping people from playing it. Buying things, sure if GW wasn't releasing anything worth a shit to consider buying that's on GW. But even with the massive gap in the market, no one really managed to truly fill that gap. Conquest, ASOIAF, Kings of War, etc. have gained some traction, but nowhere near as much as WHFB would make you think it should have been. Considering the stagnation in the player base, and lack of playing, lack of ability for GW to onboard new customers for WHFB, etc. I really think it was just a shift in the market that had occurred. Look at the other that have seen a rise and fall in popularity since, or launched since WHFB died SW Legion/Shatterpoint, x-wing, Infinity, Marvel Crisis Protocol, Malifaux, Battletech, Warmachine/Hordes, Bolt Action, it just goes on and on. None of them are/were a rank and flank game. Warlord Games has Black Powder in addition to Bolt Action, but it has a fraction of the playerbase that Bolt Action does. A lot of these are also more skirmish oriented games as well with fewer required units, not necessarily a lower bar to entry but a lower bar to owning an army and having a variety of most of the units for it.
As much as I like TOW, I don't think you're wrong on that one. The game still requires larger armies to be assembled than AoS, requires more complicated mixes of plastic, resin and metal, does not get prettier updated models, and intentionally has some favourite armies locked away in legacy. The only practical way it could compete would be to offer the older range at much cheaper prices than their AoS counterparts due to lower quality, but I think we all know that GW would never go for that.
The brettonian and tomb kings boxes for TOW are already at a much lower price point per model(even before factoring in a cost for the books and other items in those boxes) than the rest of GWs product line, and people still bitch about how expensive they are. The tomb kings box? 93 models for $290 is an average of $3.11 per model. The brettonian box is $3.35 per model, again ignoring the larger centerpiece models, books, etc. For 40k to hit that pricing, you'd need a $160 combat patrol to have 50 models in the box. Yet people were still claiming at launch that those TOW boxes were just too expensive. Even other companies aren't trying to hit anything close to $3 a model in a starter/army box.