Over the past few expansions, PuG raiding even at the Heroic level seemingly has increased in volume at a significant level. Maybe it is unstable schedules of people who have grown older, maybe it is a younger demographic more used to plug and play gaming but I think this change is observable.
One issue I see with PuG raiding is duration. Most guilds will not clear a raid in a single run unless deep in farm. Raiding takes time and Blizzard mostly releases raids with 8+ raid bosses. In a PuG environment fully clearing a raid in a single run can be tough. Many people start their PuG raids when they will have ample time and try to refill as people leave which creates a poor experience for everyone involved. Trying to arrange a second run during the lockout often fails.
I think there are two things that would clearly help here. First is to expand the skip system. While a few raids offer multiple skip points in a raid, cutting it in chunks that are reasonably easy to clear in a single run and thus letting people organize Raid PuGs that effectively run wings instead of the entire raid, most often the skip is singular and drops you on the penultimate boss which doesn't really help much with splitting the raid (remains very useful to progress on the hardest boss and even more so later in the expac or in the future when you do mount runs).
But the better option would be to change the design. I personally love raid tiers that feature two or more raids. You get to choose where you want to progress any given week, you have thematically different environments and encounters which makes the repetition of the raids over 6+ months less tiresome. And while encounters do have decent variety in mechanics, thematically the devs are often forced to repeat concepts and create bosses with no links to lore just to fill the raid. With smaller raids you could focus on the important characters of a storyline instead of featuring multiple filler. Should Blizzard considering changing the standard to 2-3 raids of 4-6 bosses instead?