Why do I have to "work on myself" to get in a relationship?

As far as I (20M) know, you should have a relationship with someone you like to be with. Every single one of us will get ugly when we get old, so what ultimately should matter is your personality.

I gained a lot of weight during lockdown, and basically spent my days gaming, watching college lectures, and eating junk food. But my personality remained the same

So, starting this year, I started pumping some weights, reading some books, graduated from college and am actively looking for a job, and noticed that I'm getting a lot more attention/compliments from women. Now, if those same women didn't give a fig for me before, why should I value/not lie/ not play then? If they didn't want me at my worst they don't deserve me now, right?