What do you mean? Sceptile has tons of great special moves. It gets Giga Drain, Dragon Pulse and Focus Blast through TMs and move tutors, all of which are fantastic moves that provide Sceptile with great type coverage.
There is no given reason for making Mega Sceptile a special attacker - only the developers know for sure. But it's pretty clear that Mega Sceptile is a special attacker because it's original form is; that's really all there it it. It wouldn't make sense to change it. Pokemon like Pidgeot changes their attacking style when they Mega Evolve, but there's a reason for it; Mega Pidgeot can spam Hurricane + No Guard as a special attacker, something that it would not be able to do as a physical attacker. Sceptile really has no reason to change.