....This is a weird program the GW2 community has created.
I believe that this stems from the fact that there really is no way to judge a persons preparedness for raids. Other games have at least a gear score, so you at least know that that person was invested enough to gear up (I would assume, I didn't play those games). This game, you can have random people showing up in whatever they happen to have (ex - wearing soldiers stats while trying to fill a dps role, or wearing rare/exotics of differing stats). The only way groups have of determining someone's willingness to invest, is in the number of LI that others have accrued (or any other arbitrary means, like the AP requirements in prev dungeon running days). Whether right or wrong, it is the method that the community adopted, to at least filter out those that were not invested.
Something to consider about training runs, they can end up being like auditions. The reason for this is because a lot of the experienced community gives back by helping to run these. You do a training run, even if it gets nowhere, you can still get noticed and invited to a guild. I understand if you don't want to do them, I refused to do them myself, but it took me a much longer time to get into raiding, than it had to.
I understand what your saying, and for investing into harder content, yes. But, for example, in SWTOR (Star Wars: The Old Republic) they have 3 tiers of difficulty for raids, Story Mode (SM), Veteran Mode (VT) (former Hard Mode HM), and Master Mode (MM) (former Nightmare NIM). The story modes have min req gear ratings, but they are not high, plus they have daily rotating group finder raids, that give a bolster up to the avg gear rating for that raid. So people who might be a bit under geared, or who don't have time to regrind gear can still experience the storyline, for all the raids and on every character. Now VT? Also a gear rating, but no bolster, better rewards, extra mechanics, but still the same storyline. And MM is just worse. Imo, the "normal" of raids in GW2, is the VT mode from SWTOR, it gates people and prevents them from seeing the storyline. But SM does NOT give the same rewards as VT. You want those rewards, go gear up and learn the fights in VT. But if you just want to do the storyline and get some basic rewards, you still have easy story mode to do. Just wish Anet would do the same thing. ie: easier raids so people can see the storyline, but less or next to no rewards, unless they do it normally or in CM.