Could anyone tell me how this 2 to 3 hour survival works?

Long survival runs require a certain amount of kills/minute to sustain life support without using capsules. Particularly in steel path - if you can't keep killing enemies for life support drops, your life support will eventually peter out and you'll be forced to extract.

Since Nekros makes enemy corpses drop more loot, they have another chance to drop a small life support pickup. This greatly reduces the amount of kills/minute required to sustain life support, and generally makes it a much smoother experience. If you aren't able to kill enemies super duper fast, it's not a bad idea to pick Nekros and make the survival mission easier for everyone else.

Long haul survival is gated by oxygen drops. Even if you're killing mobs at a reasonable rate they've adjusted drop tables to still force you to slowly bleed out cause that's what they want to happen. The work around to this is that you need a drop rate frame like Nekros to circumvent this.

Problem is that everyone wants to run boring ass optimal crap that they've ran hundreds or thousands of times over the years and they refuse to deviate. So they're telling you to be their oxygen bitch, or at least conform to their meta, or to gtfo.

Outside of needing a farm frame I think the rest of them are stupid, personally speaking. Don't take it to heart and just ignore the idiots who waste their days running the exact same mission with the exact same setup on autopilot day in and day out with no real reward to it. It's not even a challenge when all they do is run solved metas that were pioneered by people who came long before they even started playing.

Several frames have the ability to increase drops. Nekros, khora, hydroid, and atlas. I don't remember the specifics, but atlas wasn't as good for farming. Having at least two of those in a squad (and everyone sticking together) makes survival a lot easier.

Survival missions are not sustainable by design, even if you actually use the life support capsules.
In order to make them sustainable in the long run, you need, at least, one loot frame (like Nekros) to generate extra loot which also means extra life support drops.
If an already formed group is only lacking a loot frame on the squad, of course you'll get dumped if you can't fill the spot.

Everybody wants to spend hours in a survival mission until they need to pee.'

But seriously don't do this. You don't need to. There's no special reward for doing this. The reward cycles repeat A>A>B>C>A>A>B>C and so on, so there's no reason really to push an endless mission past 20 minutes, besides avoiding the extraction/mission select bits, but those are nice sometimes 'cause it allows you to go and pee or whatever you need to do.

I repeat: There's no special reward for doing a 3 hour mission. There's no point in doing so.

Short and simple people are kinda dicks so my recommendation is if you want to do hours long survivals do it either on your own or with friends and do it for cracking relics and materials like the one on lua I one did a 5 hour one with nekros and my friend had revenant no idea how I survived the high levels but I did

If you want to do long survivals honestly do them solo the benefits in that is u can do whatever u want however long u want and you can pause to go toilet eat food etc and come back to continue ur run

I'm that one person that loves high rewards for low effort gameplay lol the less i play the better. so when I'm asked to be nekros, that's the best for me cuz i get to just watch netflix or youtube and mindlessly run around desecrating lol