How do you prevent your website from not functioning over time for legitimate users, though? I'm a Sysadmin & not a coder or developer, so the tricks you can do

How do you prevent your website from not functioning over time for legitimate users, though? I'm a Sysadmin & not a coder or developer, so the tricks you can do are a little foreign to me. Can you provide examples? Why don't Adidas/Nike/et. al. do this to fight the likes of sneakerbots?