You need to be able to perform long division to take quotients in algebraic structures, e.g. polynomials. Yes, Wolfram Alpha can probably do it, but not always.
You don't need to understand long division to be able to do that. Long division is over the integers. It's got a weird notation, and I never learnt it.
There isn't any reason for 99.9% of mathematicians - even in abstract algebra - to know long division.
As a kid who chronically forgot to bring her calculator to school for about 12 years straight, I can now do long division well enough that I sometimes do it rather than get up to fetch my phone from the other room. It's also how I do division in my head.
I did pursue mathematics academically but I don't know if it ever came up in university math; more so in physics and computer science.
EDIT: apparently what I do is "short division", which is just long division but you don't write down all the steps.
After looking it up on Wikipedia and seeing the various notations used (most of which are awful IMO) I get the hate on long division, though I never felt anything like that.
It may be because it is familiar to me, but the notation I learned in school in Austria feels superior or at least less irritating. I guess German schools use the same.
Why the heck write the divisor first?
This is news to me that people can't/don't do long division. It's simple. I use it regularly to estimate quotients--just run the process to a couple places in your head.
It's much easier in base 2 than in base 10. Similar to the multiplication tables, the table for base 2 is just the 2x2 matrix at the top left corner of the 10x10 times tables.