I would say we disagree with the premise of the question. Mathematics is not a singular noun. It’s a plural. It’s the field of all mathematics. Therefore you preserve the “s” because you abbreviate the singular and re-pluralise it.

So somebody in the UK might (not commonally) say “it’s a math(matic) concept”, but more likely to say “it’s a concept from math(ematic)s” or “it’s a mathematical concept”.