At the risk of getting this thread closed Trish was hot as fuck with some cool matches(I only really liked the WM22 Mickie James match tbh) and that's why we remember her. Lita was also hot and a spot monkey. Both were the top women during the biggest boom period in wrestling, that contributes a lot to their popularity.
The women now are much better wrestlers overall and put on better matches. I'm not the biggest fan of the WWE product now, but their women's division is probably at it's best right now(mostly thanks to some NXT matches).
I think more than anything else, both women were involved in some form or another with the guys (popular often, like The Hardy Boyz), and that definitely helped them become more well known.Shoot, when Jeff Jarrett's music hit, people were standing up because Debra was coming out and the men wanted that. Look at a recent example from modern WWE with AJ Lee and Daniel Bryan. If she stuck to her same ol' gimmick and perhaps stuck with Primo, she doesn't get near as popular or the attention.
Another big factor, to me, is they took moves from the guys. They took samoan drops from Viscera, chokeslams from Kane, so on and so forth. And looking sexy in their outfits helped too. Lana and Summer Rae cat-fighting got more attention and reaction than the bouts with Sasha Banks and Paige did several months ago. And fans like that non-sense, bad or good however you want to see it.