What VineBigBoss and Caiden said. Though I'm sure there might be more to it than even that. I kind of want to research all the reasons for the lack of costumes, myself.
I'll admit, I was a little disappointed; I know many a-fangirl was happy over DMC3 Dante having a shirtless option...
...Personally, I'd give my eye-teeth for DMC4 Dante to have had that option, as well. XD
Perverted-ness aside, I also would have loved for them to have a variety of costumes for Dante: Be it his DMC1 and 2 costumes, or a new, alternative one (because let's face it, as cool as it would be to see him in some of his past garb, wouldn't it be refreshing to also see some new costume ideas?)
But in any case, the lack of alternate costumes isn't too big of a deal to me; it's not a deal breaker, or anything. It's just sad that something the series is well known for got left out.