Why are people not honest anymore?

I’m a female in my mid 20s, i’ve been single for 3 years. Every single date i’ve been on recently with a man - they just want sex but they’re not honest about it. I’d say I have very high standards and i’m very upfront and open about that. Over text these guys will act super sweet and kind - then it gets to the first date and they tell me everything I want to hear. They tell me they’re also looking for a partner and a long term relationship. Then when it gets to the end of the date they just want to have sex?? Like why not just be honest and say hey i’m only looking for something casual/looking for sex. Like why the hell say you want a relationship when you clearly don’t! I just don’t understand the mentality. It must get tiring surely