Leave your wet towels on the bed. Marathon the entire 7 seasons of Buffy over a long weekend. Never dust your bedroom's ceiling fan. Eat chili in bed. You can live at the most disgusting level of existence you can tolerate, and it's completely fine. There's no one else to be considerate towards except maybe your roommate ... who you should have picked to live with because they are equally disgusting as you.
Without having another person present to question your logic, you're free to wake up at 3 AM and practice the Cupid Shuffle just to see if you still remember it for your upcoming friend's wedding. Have an imaginary conversation out loud of what you SHOULD have said to that coworker who insulted you. Even with a super accepting partner, just knowing you are being watched will change your behavior.
As a single person, you can't fill your social interaction quota by Netflixing with a partner so you're more likely to go out and meet people. Between online dating and blind dates, you're introduced to people you wouldn't normally meet. Dates provide you an opportunity to hear a person's entire life story. In what other situation can you approach strangers and ask them strangely intimate questions? Even if it doesn't lead to anything, your worldview is at least slightly expanded by meeting them. All of which is convenient because ...
People probably should be interested in other people regardless of their relationship status, but when you're giving out single vibes, people are going to respond to them. You can spot a single person walking into a bar because they ever so slightly scan their surroundings -- there's an openness to strangers that you put out in the quest to find a sex partner.
Ideally a romantic partner challenges you but without someone constantly in your life asking you why, you can go about presenting your best face to the world and hiding your dark, bad shameful bits that only come out in the most intimate of human relationships. Also you have more time to work out your own issues and blah blah boring self-improvement time blahs.
Dating apps and sites are terrible to use, but the point isn't actually using them -- it's being culturally relevant. If you're in a two year relationship, you've already missed out on Tinder and all the Tinder-related conversations. Even if you're in a six month relationship, you're missing out on Bumble. As a singleton, it is your right to laugh extra loud at that SNL dating app sketch when you're watching with your coupled friends.