The brochures paint a warm picture, all fun and games. Neutering is painless, quick, simple! But as with any surgery, afterward the patient has to take a week or so to recover. The patient, in this case a puppy, has to avoid strenuous activity and stay in a relatively clean environment, which makes perfect sense, unless you're a puppy.
What do puppies do? They run and jump, eating the shattered pieces of shit they crash into. They roll around in the mud, pick fights with big dogs, chase cars. They are not concerned about stitches and infections. They cannot be reasoned with. Puppies are fuzzy little monsters, hedonistic and hellbent on the annihilation of the planet.
Needless to say, locking such a creature inside an apartment for a week is… challenging.