Why did the military mutiny collapse in Russia in a day?

The Wagner leader couldn't get the Russian security forces to defect to his side because Putin enjoyed strong support in Russia.  It would be very difficult to dethrone a leader that had majority support in the country.

Let's take a look at Putin's approval ratings before and after the Ukraine war.

Putin's approval rating was at 71% before Ukraine invasion.

Putin's approval rating increased to 82% in May 2023 after Ukraine invasion.

Let's take a look at how supportive the Russians are towards Ukraine invasion.

75% of Russians still supported Ukraine invasion despite the US and EU sanctions because they knew they faced a significant threat from NATO if Ukraine joined NATO as NATO would install missiles defence system in Ukraine.

https://sg-stock.blogspot.com/2022/03/the-hard-truth-russia-is-not-wrong-to.html