Unless people are playing with guilds or friends, keys are now abandoned quickly if people do not think the key is time-able. This is because untimed keys in Shadowlands only offer each player a 20% chance of actually getting loot. Thus, the vast majority of players in PUGs do not see a reason to finish struggling keys.
Even worse, key holders have learned just how bad it is to untime keys and now set ridiculous ilvl requirements like 200 ilvl and 700+ raider IO to do a +6, I know this, because this is what I do for my +6 keys. This is what my friends do. This is what everyone in my guilds have done. This happened in BFA, but it wasnt nearly as bad imo.
I appreciate the value and gameplay with regards to doing timed dungeons. I also think there is room for dungeon gameplay that rewards players who have spent many attempts and wipes to finally down bosses whilst mastering their mechanics. There is literally no worse feeling than finally downing a high key after many many many attempts (even maybe because of a teammate) only to not ANYTHING at all at the end of the dungeon besides 95 anima.
If loot is not to be offered, perhaps a currency of some sort that has SOME value.
Personally, I have always best learned boss mechanics through failure. Only through repeated deaths and dying during high keys do I master the most difficult bosses in WoW.
However, due to the consequences of not timing high keys, keys are abandoned now after one wipe. Instead of powering through a boss after several attempts (this is how players LEARN mechanics), players would rather just leave and hope to be carried in the next dungeon. Or just do a +10 mists instead.
Currently, only high keys really engage me as a player and really punish me from not doing mechanics correctly. Bosses like the 2nd boss of spires or the 3rd boss of plaguefall only become difficult during high keys. Regular mythics are too easy and mechanics can largely be ignored outside of heavily punishing effects. Players are not learning how to do these fights correctly in regular mythics.
Lastly, gearing is best done by spamming keys a player does not find challenging. Instead of doing challenging, engaging content it is far better for me to do easier keys that I know i can time easily thus my group can get more loot.
Overall, the dungeon gameplay loop has shifted overcoming high M+ dungeons (this often requires team communication and LEARNING mechanics) to spamming the highest possible key a group can overcome easily.