Why I don't particularly like the name Grant:
Grant. Grunt. Thuggish character that used to be on EastEnders. Seems a bit dated.
Dislike of surnames used as first names in general. Because they're always a bit ambiguous, you know how on some official forms they write Surname, First name. Feels like the person hasn't got a real first name, but 2 surnames. Why, when there are so many lovely names available?
Also Grant is not a very mellifluous sound. Very short and basic. Dislike of names beginning with Gr... in general. Grrr.., grim, grumpy, grizzled, grey, grime, anGRy, it's a harsh sound in general. Although I admit Grace has grown on me in recent years, probably because of the lovely meaning.
I don't really hate it though, there are worse names out there. Fine as a middle.