Mythic is 20 people maximum. You can't have any more go into mythic mode. As for heroic... they should be taking more people. The more people you bring into heroic the more gear the bosses drop so... They're really just screwing themselves. But mythic can only have 20 people.
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I know plenty of people who have had cancer longer than they've lived without it but they don't stop trying to get rid of it cuz it sucks the life out of them just LFR sucks people out of attempting to raid. The game should have some incentive to actually get better and progress your skill. Also pugging is a thing you can do. Back in the day, casuals who could only play for a couple hours on occasion would find pugs to join. Maybe your Saturday was suddenly free. Log in and start a pug. Easy peasy. Very little actual time commitment other than the commitment of doing the equivalent work of wiping your own ass in WoW form in order to find 9 other people to raid with. Hell, I've seen people on my server asking for fill-ins to mythic raid progression. Just work on your skill/gear and find some groups to join without a committed raiding schedule. It isn't hard. LFR takes away the incentive to do that.