Why is NL cash still popular?

maybe nlhe cash has just historically always been popular

But recall 2003 when FLHE was still the most popular game online, especially in Europe... then NLHE (non-Zoom specifically) has somehow been dominant for 12 years despite facing the competition of a few innovative game types. There might be something inherently superior in it, maybe the simplicity of naming and graphically representing sets of two hole cards.

I know, the Moneymaker boom happened, but Party's marketing team was also ready to market poker. Maybe, if the 2003 WSOP ME winner had been a pro, FL would be in the mainstream for longer, who knows. It's a great action game itself, especially shorthanded, it doesn't allow to play with 18/14 stats without bleeding money really fast.

The biggest difference I can find between FL and NL is the bigger variance of the latter, but then it's not clear to me why a game with even higher variance hasn't taken over yet.

It's also relatively simple.

I don't think it's too difficult.

1 - NLHE is a lot simpler to learn and figure out which hand you have.
2 - NLHE is the mainstream variant these days, and people love to follow trends.

I understand that people don't like to spend time figuring out an Omaha hand (though the hand strength is written explicitly at a few non-Stars sites)... but still, I was wondering why 6-max/HU hypers failed to take over - they're even simpler.

Perhaps that was because they're a bit too slow / uncomfortable (It's impossible to sit out in tourneys for long without losing chips) and they still don't have nearly as much variance as MTTs.

Spins are both faster and swongier, and it looks like their trend has just been slow to form (for some reason, hardly any Stars SnG reg had been discussing Twister until it was replicated by Rational Services), though Stars have reported that tournaments are already accounting for most of their revenues. I'd say that this trend eventually take over, but Stars themselves might stop it or make it short-lived by rolling out even more exciting and thought-out game formats.

There's no doubt that NLHE will continue being dealt at small stakes in land-based casinos because the ease of dealing and determining the winner matters a lot there. In the online setting, there's more room for fantasy. At high stakes, though, the rake is big enough anyway, so rooms can surely afford to deal HSPLO, and as far as I've heard, the biggest live games are usually with 4 cards due to the bigger gamble in the format.

Interesting question. I think one of the reasons is marketing as you suggested. But I'm not sure if I agree with omaha being more gambly from a rec's point of view. NLHE can be played in a gambly way if you want to and I doubt that rec will see the difference. Omaha is also much harder to learn.

and omaha much faster takeing away money if you in down side ♦

It is because NLHE hits the sweet spot in terms of the number of hidden cards leaving room for maneuvering. Omaha is a very very simple game compared to NLHE once you know the mechanics of it (which, I admit, is more difficult in Omaha). Add to that the fact that 100bb is a totally inadequate amount to play PLO. In effect, too many plays are autoplays in the game. This adds to PLO being more akin to Spin & Go than to CG NLHE. An even simpler game is Omaha Hi/Lo which, on the surface of things, is even more complex than straight PLO.

In PLO u pay 3 times as much rake as in NLHE.

But then again, 5-card Omaha is surely more interesting from the scientific viewpoint.

Disagree As YohanN7 mentioned, in Omaha games (at least most of them) actual gameplay <100bbs is poorer than in NL, it's theoretically shallower despite its surface complexity. Just because equities run so close, so many hands have a lot of it on most boards, that difference in EV between betting pot and betting 1/2 pot becomes huge. Therefore a lot of the times theoretically you can play only pot or fold, otherwise you're making pretty large mistake. Somewhat similar to FLHE, which has been pretty much dead for several years now due to impossibility to find big enough edges to beat the rake. In NLHE player has a lot more ways to split his ranges and build his strat.

I understand recroplayers don't know any of it Just interesting common misconception imo. May be I'm mistaken, I haven't really explored PLO theory very deep.

Or maybe it's solely the fault of poker sites that keep neglecting PLO in their promos

I believe it starts the other way around: PLO is less popular, hence they make less to none promos for it. And since there are no promos - new players are not aware of existence of the game until they start digging deeper into poker in general, which often doesn't happen at all. Circle completed