What’s the reason people waste wine with spitting it out at wine tastings?

What’s the reason for spitting it out? I’ve never actually been to one yet but I know it’s common for you to taste the wine and spit it out. I could drink glasses of wine and be fine so getting “too fucked up” or whatever isn’t an issue. Plus a lot of wine tasting events you have to pay for and they aren’t exactly cheap either (I guess that depends where you are and where you go). It just seems like a huge waste of wine (especially expensive wines that they hold so valued) to essentially treat it like mouthwash. If I’m going to an alcohol event, I actually want to be able to enjoy the alcohol, especially if I’m paying for it. With the amount of money going there I could have bought a few bottles of wine and enjoyed it at home. I understand it’s the sentiment of trying new wines and seeing what you like, I just don’t understand why we need to waste it. Some of these bottles are $100+ and you expect people to just spit that out and waste it? Could someone please help me understand?