Hello!
As far as I know, when creating content on the Roblox platform, you automatically sign away your copyright to the Roblox Corporation. Fair enough, but I’ve seen scripts and models including licenses such as MIT, Apache and GPL and I wonder if they still legally apply even though the content is not legally yours, but Roblox’s.
Thanks in advance 
Licenses don’t do anything in Roblox. Especially if you found the script in free models.
The content you create is legally yours, you own the IP and license it to Roblox. Roblox has this in their TOS. Licenses are what they are, and need to be enforced by the one who issues the license. Some licenses just explicitly say what the person can do with this content, some allow the end user to do whatever they want. The reason you would want to explicitly say what someone can do with your work protects the person who uses it.