The (1) in make(1) corresponds to which section of the manual[1] make is in. This is useful in some cases to distinguish between things that might be in multiple sections like printf(1) the user command and printf(3) the C library function. When everyone knows what's being discussed, I think it's mostly people trying to give a shibboleth that they've read the fine manual.
[1] - https://en.wikipedia.org/wiki/Man_page#Manual_sections