I can agree with you in terms of readability, even as a mathematician. For example, the list comprehension syntax mirrors the mathematician's "set-builder notation," so it feels very natural.
However, consider something like a "max", "min", or "argmax" function. Like map and reduce, you can implement this in terms of reduce, but I don't see how you can implement it in terms of a list comprehension. Or consider something like an RPN calculator, which could be implemented as a single reduce call whose initial value is an empty stack and whose input list is the list of RPN tokens.
It seems that list comprehensions can do less in a very objective sense and couldn't be used to replace reduce without other supporting characters. Python has those supporting characters, of course, so there's a good 80/20 argument for favoring list comprehensions over a more opaque call to reduce.