Why has every service started harassing and locking out legitimate users?

Every single time I try to log in to some account, be it Twitch or Mailgun or anything, using my correct passwords, they display a message saying that they "need to verify" that it's really me and have sent a code to the e-mail address I used when registering years ago, long abandoned and inaccessible.

Why is having the right password no longer enough to authenticate oneself? It's even in the name: "pass word". You need the "word" to "pass". That is what authenticates you.

If somebody enters my username and password, especially if it's on the first try, it's going to be me and nobody else.

I've lost access to so many important accounts this way. Never could I have anticipated that they would start doing this idiotic nonsense in the future (now the present). A password is a password. If you have the password, you are the right person. That's what a password is.

Even beyond the frustration of never again being able to log in to my accounts, in spite of having the (strong) password I saved when registering and have kept ever since, this bothers me on a philosophical level as well. You can't be sure of anything anymore, it seems. It's never enough. There's always some new hoop to jump through. As if they enjoy putting up these obstacles to frustrate their users...