In the 1980s a British Airways 747 flew through volcanic ash and lost all four engines. So just having more engines may not always be the solution, as in suitably unlikely circumstances you can still lose all of them.
(In that case they were at cruising altitude, so had time to handle the situation and relight the engines).
"Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress."
It depends on what is causing the failure and how situation evolves. Let us take British Airways Flight 009 as example, the wiki says that all engines failed, all engines were restarted and engine number 2 surged again and was finally shut down. So even this awkward situation was relaxed a bit by the additional safety margin.
Most airlines avoid nowadays the invest into maintenance of four engines airliners. Others have prefer the additional transport capacity and margins. Lufthansa has it's own maintenance branch "Lufthansa Technik" and doesn't need to handle extra costs. Emirates needs the huge capacities of the A380.
PS: The 747 can and does - if necessary - ferry flights without passengers and only three engines. Not possible with twin engine planes.
I think it's more that they needed the prestige of having the biggest planes, offering a whole bedroom with shower etc. It goes well with their ultra luxury image.
If it's just about seats that can fly smaller ones with the benefit that they can operate more frequently and thus attract more transit passengers looking for a good connection. That's their main market.
An A380 is quite a hassle because most airports can't even handle one.
That airports are usually not an effective destination for the B747/A380.
Connect major hubs like FRA with JFK and it makes sense. You need capacity, it is a long route and slots are rare and expensive. And for Emirates the hub concept is crucial.
But yes. The luxury thing is also part of their show. But it fills the plane ;)
There's many more hub airlines though that don't use them. Is Emirates really that different? Or are they kinda stuck because they went all-in.
Many operators dropped the 380 during COVID. Makes sense but they never took them back on afterwards and passenger numbers are higher than ever before now. The A380 is cool but it was built for the past not the future.
(In that case they were at cruising altitude, so had time to handle the situation and relight the engines).