Telling people that they need to learn boring prerequisites before they are allowed to learn the next thing is exactly how you kill motivation. This strategy works if you have a fully mapped out curriculum that is planned as a whole and a societal expectation that you go through the entire thing, it doesn't work for independent learning.

For independent learning, motivation is the key bottleneck and your goal is to make people organically motivated in calculus after learning that their calculus knowledge is lacking.