The way alot, aswell and noone are combining is expected given how many other words we don't bat an eye at went the same way. "another" is the perfect example, it's just "an other" combined.

It's sort of the reverse of what happened to words like apron and newt.

The division and bracketing of phrases changes over time.

"An apron" is the modern usage of the word "napron", and a newt was originally called an eute. The grammatical need for "a" and/or "an" resulted in the root word being rebracketed and changed.

Apart/a part is another one.

it's all just made up. you can see old writings without spacing. or punctuation. you can't even define what's really a word universally. people just decided what's what and standardized it at one point just for some consistency. that doesn't mean things won't change; they most definitely will.

I recall "noone" being taught as acceptable by my english teacher back in 2004. That being said, she's also said some things that ended up being very wrong

I always imagine Peter Noone of Herman's Hermits whenever someone does that.

"Noone thinks I have a lovely daughter." Yes, Mrs. Brown. Noone does.

Ampersand is another good example. "&" was considered the last letter of the alphabet for a while. Schoolchildren would recite the alphabet and finish it with the phrase "and, per se and" ("and, meaning and").

The words got mashed together over time and the word "ampersand" was born.

No body writes noone as one word because there's a similar word written that way.