I see that very few explanations have been given here in regards to the so-called 11:11 phenomena, so I've decided to give it a shot. Feel free to comment, I'll try to answer any questions, disagreements, or anything similar. I'll also link a web page which explains this in more detail (I'm not affiliated with them though, but they're probably the most accurate sources for now).

If you look around the internet for answers, you'll run into numerous sketchy spiritual websites and vague explanations. Most of them are based on highly superstitious beliefs, dogmatic nonsense, etc... However, it turns out that reality is indeed crazier than fiction. Giving a full explanation on the causes of the 11:11 phenomena would be too lengthy for a reddit post though, so I'll try to summarize everything. I want to also let you know that I used to be a skeptic and atheist, but certain events which I cannot deny nor attribute natural causes no matter how much I try have made me change my mind.

Why do you see 11:11 everywhere?

They're called prompts. A type of semi-material well-meaning beings use them to get the attention of us human beings. These quasi-material entities are called Midwayers.

That escalated quickly. Are you on drugs or something?

No, although if that was your initial reaction I don't blame you. I wouldn't have believed myself a couple of years ago either.

Ok, so who are these Midwayers and what do they want from me?

Midwayers are one of the many entities that live in our universe. They're kinda like our spiritual cousins and live here with us. I don't want to get into too many details and I'd prefer to stick to the 11:11 phenomena which I have personally experienced, and Midwayers, with whom I have interacted with. These two are just the tip of the iceberg, but I can't be 100% sure of everything else, which nonetheless is very likely to be at least partially true. So Midwayers, usually called angels by the mainstream "spiritual" community, have our best interests in mind and continuously work to improve the condition of our world, mostly by helping us, its material inhabitants. 11:11 is a "trademark" of sorts for them, so they use the number to draw the attention of humans. Why? There's many reasons. They might want you to get involved, to get to know them or to assist them with something. You might have a particular talent which would be useful, you could be an important figure now or in the future, your Thought Adjuster (long story) wants you to get involved, etc.

Why 11:11?

1111 is a special number for them because that's the exact amount of Midwayers that did not rebel during the Luciferian Rebellion (even longer story) which is responsible for many of the things that are wrong with our world.