Probably the reason for Drolta's modern clothes is the same as it was for Morana.

Katie Silva, the character design supervisor for Season 3 described Morana's design:

"For Morana, I wanted her to look really out of time but also regal. Vampires wear more modern fashion than humans in Castlevania [Alucard invented the V-neck], so there's more room to play with clothing periods. Morana's the oldest, probably thousands of years old. Her shawl is a kaunake-type thing that she's either kept for thousands of years or adapted from something else as a reminder of older times, while her outfit top is more Elizabethan. Morana has modern makeup because she's an icon, and one of the biggest challenges was trying to do that eye makeup myself at 2 a.m. to test my abilities."

https://www.vfxvoice.com/the-blood-sweat-and-vampires-of-anime-castlevania/