You're not good. You, your bedding, your clothing, your carpets, furniture, keyboard, mouth, hair and everything carries bacteria and fungal spores. Unless you wash your hands after every single contact with every single item 24/7 and you wash your sheets daily and use disinfectants then you are carrying foreign bacteria and spores onto the mat. 99.9% of the time this won't matter. Just like if I very ocassionally don't get to shower the minute I get home won't. Sometimes it might.
How do you think infections get onto the mat in order to give people infections if merely washing your hands a few times during day is enough?
How does showering at the facility directly after training rather than later offer more protection to training partners than showering before training?
Most of benefits of showering after training are for the person showering. Being clean before you train is mostly for your partners.