Why does Roblox pester me about being a robot?

It was my first time making a profile. I went and put in my username and password. Then I tapped I’m not a robot. It made me do the “test” and I passed, but every time I go to login, it I have to do the “test” to prove I’m not a robot. What exactly does this mean and why do I have to do it over and over again?