One of the reasons for the brake pedal to go to the floor is due to leaking brake fluid. As when you depress the pedal the fluid leaks out and does not build any pressure. This leads to the pedal going soft or to the floor.
Inspect to see where the leak is coming from. If the fluid keeps leaking but the brake reservoir is still full then the issue is not a leak. It could be a faulty master cylinder. Typically, the master cylinder will have bad seals and won't be able to build pressure.
Here is a helpful article that covers the common issues:
I have attached diagrams for your reference.
Please let me know of any questions.
Images (Click to enlarge)
Saturday, October 9th, 2021 AT 7:12 PM