Imagine how much unnecessary time would be added to a course about series if the lecturer had to write sum() instead of ∑ every time. If you find it hard to remember that ∑ means sum, math might not be for you, and that’s fine.
it's not so much remembering what ∑ means insomuch as that it's completely impossible to google the first time you run across it. It'll be in some PDF that doesn't allow you to copy-paste the symbol and you won't know what it's called. Rinse and repeat for any of the million symbols mathematicians use, never mind that loads of symbols are context dependent even if you could google them.
I hope mathematicians have a better reason than "it's tradition" for making the entire field completely opaque to anyone who hasn't studied math extensively.
Basic notation like sums is covered in every undergraduate math course. Any non-standard notation will be introduced by the author using it. Nobody is trying to obscure anything from you.
