Let's put it this way: you can't always get what you want. Unless you are on a high/full population server, your pool of players capable of mythic progression are already low (even high population servers can struggle with this, especially if the faction balance is lopsided). Notice I said capable, not good. The skill range runs wide, and while every guild wants the best of the best raiders who are deemed good, that's never going to happen. Also, people's definition of "good" and "bad" is pretty varied, and while a person can be good for another guild's demands... they can be bad for another guild's demands.
I used to raid top 30-50 US, and even we had issues with what we considered bad players for our level of play. A lot. This is why we always had a large flux of applicants if we could, but eventually the server population dwindled to where we couldn't keep up recruitment to where we wanted. Therefore, we had to do raids with people we normally wouldn't want, but we didn't have a choice if we wanted to raid. Eventually the guild disbanded because server population basically disappeared and the effort was not worth the squeeze at that point.
While in a much more casual environment for raiding, I still do mythic progression (albeit much slower versus full clearing in the first couple weeks). I'm on a high population server now, but we still have issues with recruitment and getting players that are good enough for our standards, even if we set the bar lower than what my former guilds would take. As it stands, it's still a chore to maintain a roster to ensure there's enough for raid, let alone how picky we can be with applicants. Even then, there's a clear difference in the roster between the strong and weak players.
Back on topic, the ROI when giving gear to the weak players tends to be low compared to giving gear to the stronger players in most cases. I said most, as there can be diminishing returns feeding all the gear to one player if the upgrades are tiny. However, that should be the prerogative of the guild/raid: assigning loot where it'll be used the best. Despite conjecture in some responses in this thread, sometimes the best option is giving a piece to the bad player(s) in your group over the good ones as the net gain may be more. Just funneling everything to one person or several good people at the start of the tier is generally a solid plan and the best ROI you can make for the drops versus giving the gear to someone who tends to die early or screw up more often on progression.
All this ties in to one of the major weaknesses of PL over ML: you cannot min/max your group for progression as easily as you could with ML. Despite the snide remarks, every raid has good and bad people in it, it's just a relative matter. If you think that even at the top the discussion of who gets what based upon skill/performance isn't made, you're woefully ignorant.