Approaching the issue from a pure math perspective.
We operate under the assumption that for every PVP invade we launch someone will get a PVP defend. If we win, they lose. If we lose, they win. Makes good sense.
If everybody played the same amount, and it were equally distributed, everybody would have just as many defends as they have invades. But it doesn't quite work that way. A quick look at the leaderboards show that in the top 100 everybody has a lot more invades than defends, generally at least twice as many. Which means either there are others with a lot more defends than invades, or some aren't getting tracked.
If the goal is to maximize resource gains (assuming you know you're not going to be high enough to win arcanes) you're going to want to be in the second group. So how do you increase your number of defends (which are free resources), and ideally win more defends than you lose (for 3 glory instead of 1)?
That is the question this bug, side-effect, exploit answers. People found a way to increase their share of defends. But if more people do it though, it will dilute the defend pool anyway. Imagine there are 5000 invades happening, and 10 clever folks figured out how to get them. So 5000 split 10 ways, each get 500. Nice! But if 200 people do it, it is reduced to 25.
The other way is if everybody triggered more invades (more players won't change things since new player adds invades, they also consume defends, so it averages out). Even if they were intentional losses, it would increase the number of defends in the pool. For example, imagine there were only 100 players and each did 10 intentional losses a day (like going in w/ empowered Elspeth and sacrificing on turn 1 to lose). In that case each of the 100 should (on average) get 10 defense wins. Simple on small scale, unwieldy on a large scale.
I think what we are seeing, partially, is a combination. People are intentionally losing to lower score, which matches them against others with lower score, who are also intentionally losing. So they are effectively feeding each other defend wins for 3 glory each. Is it easier than doing it the right way, probably. Is it faster, probably not. With guild, event, invade, rival, and revenge glory generating as much as 16 glory for a single win it adds up pretty fast.