Corruption and Crimson spread rate ramps up to eleven in Hardmode, but the bigger thing is that this is in the desert. They spread *extremely* fast through desert because every block is corruptible and there’s generally no holes or stuff they have to cut their way through.
If you haven’t noticed, Hardmode also spawns a new corruption or crimson biome in the world and you happened to get screwed over hard and have it spawn it in like ten feet of your home base.
The quickest way to protect your home base from the Crimson is to buy a bunch of dynamite and bomb around the areas you need protected, make a 6 block tunnel to keep the corruption/crimson from passing over. I recommend doing that ASAP seeing as how close the corruption is both next to and below your base.