Originally, maths/mathematics meant "things that are taught", like physics meant "natural things" and similarly for other such names.

However, nowadays a word like physics is understood not as "natural things", but as an implicit abbreviation for "the science of natural things". Similarly for mathematics, mechanics, dynamics and so on.

So such nouns are used as singular nouns, because the implicit noun "science" is singular.

"Maths" is short for "mathematics". The latter is not plural and can be substituted into this quote with no other alterations.

Yes maths is singular, just like physics. We would say in the UK "maths is hard, physics is also hard"

Maths is like physics