Why does bards autos proc thunderlords but lulus doesnt?

Bard still needs a couple AAs to proc it (or an AA+Q), and that's assuming he has a meep available, which he doesn't necessarily.

Lulu on the other hand would almost always be able to proc it in a single AA, which would be a bit too reliable.

Because it costs Bard his Meeps when he Auto-Attacks. Lulu's Passive is always there and has zero cost.

Bard's passive applies spell effects while Lulu's doesn't.

Considering this means that Lulu can't apply Rylai's Crystal Scepter's slow and Liandry's Torment's burn on every autoattack, I'm quite willing to accept that.

Pretty sure it does. 1 of Pix's bolts counts towards Tlords last time i checked it, unless that was remedied back on PBE.

I wouldn't remember since i prefer Windspeakers.

Kayle E counts for 2 parts of thunderlords as well. My guess is that Lulu's extra damage is considered part of the attack itself since it's always active while Bard's meeps count as a separate spell since he doesn't always have them. That seems to be how Riot determines if something procs thunderlords or not. Need to activate an ability? Then it counts. Always active? Doesn't count. That's why Teemo E doesn't proc thunderlords but Brand passive does.