Interesting, I buy keys from G2A regularly and haven't lost access to any titles yet. If this was a significant problem I'd expect to at least have a few lost titles out of dozens I've bought personally and for friends.
Per the article, G2A claims only ~1% of transactions on their site have problems like that. So assuming they're not lying, it's no surprise that you haven't lost any titles yet.
Also, they have no way to check the status of the keys. So, if a user doesn't report an issue, they'll never know about it. Given that the article says that most users don't notice keys being revoked, it wouldn't be surprising at all if the majority of issues never get reported.
I think the devs claiming that users simply never notice that the license was revoked are the ones who are lying.
Every time that's happened to me (for example, a time-limited version of a game or a beta), Steam presents a notification that the game has been removed from my library.
Point being that if they player has already moved on to other games they may not care, i.e., G2A never find out, and they're numbers are wrong (assuming they're being honest in the first place, which is a big assumption.)
They've always been this way. My opinion on them is not new.
A bunch of esports teams dropped them as sponsors years ago after realizing they not an honest business. Their buyer protection service (G2A shield) is a scam. There's also this fun AMA they did
https://www.reddit.com/r/IAmA/comments/5rg9mo/we_work_for_g2...
