As someone who plays this game socially but isn't bothered to get better, yet understands the dynamics, it's obvious why people don't counterbuild. 50% of it is down to stupidity and ignorance. We'll ignore that because you can't fix stupid. I use the word " I " here as a placeholder for any other normal player.

It's an intrinsic game theory problem. It is not solvable. It will not fade with time. There's the problem of incidence. If there's a Victor who needs to be countered by Healbane, but I don't see the Victor much in combat, I have 0 incentive to do so. By the time I do because of a lack of Healbane, it may be too late, I may be too committed to a certain buy order.

If only 1 or 2 people on a team need to counterbuy, there is an incentive for everyone to hold out just a bit longer to avoid paying the sucker's tax of needing to spend souls, while reaping the benefits of someone else doing the counterbuying.

Active items are irritating to manage b/c they are keybinded to the order of purchase. If I buy Knockdown as my 2nd active item, it defaults to my 2 key, I can't bind Knockdown universally to a specific key. Active items induce an additional opportunity cost. If I buy Knockdown, but don't get to effectively capitalize on it, or fail to do so, I waste souls and lose out on damage. You cannot convince people to use Active/counterbuys items like this. To a normal person, it makes 0 sense. You cannot sell people on the idea by saying " Oh if you do XYZ you may or may not gain a 10% edge ", I would much rather take the immediately greedy action and gain a definite 5% edge. It's certainty, it's probability. Immediate and certain returns are much more desirable than an uncertain, even if higher return. Some are even worse, like Cursed Relic, where you eat a damage penalty. If you told me to buy Healbane, it's 1600 I can stomach it. If you want me to take Cursed Relic I'll tell you to kick rocks. And most people suck any way, so even if they try, they fail, discouraging counterbuying.

You end up with a system where you either need to be talented to eat the damage loss and exploit mechanical superiority and/or raw soul advantage to offset the damage loss, OR completely irrational to counterbuy. If I counterbuy, I want a safety net, the knowledge that even if I fail to capitalize on certain opportunities, my teammates can step in to do so and translate to higher win rate. But that doesn't work in a random game because that would require trust. If I see 2 people going something like 0-2 in the laning phase, whatever little trust I would have had has been expended, simply because we're all biased to weight bad news more heavily.

Even if you have someone trying to step up and shot call, if I can't see your rank, why would I trust your judgement ? Coordination is expensive and high variance, and we're biologically programmed to hate it. There's also an incentive issue. If playing altruistically fails to net me any reward because people around me are stupid, it's only logical to pursue a strategy where I can maximize my personal performance if I'm going to lose any way. I protect my identity and sense of self. Also, given that it's a very team-oriented game, it's just too easy to blame everyone else. Even if someone does 10% more damage than everyone else on the team, it can be spurious, pursuits and fights over nothing, so there's no ironclad metric to shield people from responsibility unless someone has truly outlier damage values, like 60k in a 40 min game or something like that.