There’s sooooo much porn out there. Imagine the hottest women you can, performing your absolute favourite kinks and fantasies, it’s a few clicks away, free and nearly unlimited. It’s pretty hard for women in real life to compete with that.
Most of us have natural sexual attraction to other (real-life) people, but if the mind becomes conditioned to getting off when ever it wants in front of a computer screen then that can cause problems in real life situations.