balancing/alignment/camber/toe adjustments, absorbers possibly even spring, badly damaged driveshaft/tie rod/steering rack/wheel bearing. check all those, it'll be either 1 or a combination of the items i mentioned

the bigger problem is please spare that 5 min to look at your tyres once a week, or once every fortnight at least. cannot imagine how neglected your tyres are if one of them can be completely botak while the other three are ok. remember. tyres are the most important part of your car

5-15k km, not months.
time ages all tires, however tread reduces the more you drive.

wrong rotating method
and yes as mentioned, please spend time to check your tires oftentimes, and not wait until they get uneven wear/balding and start to panic

what are u driving btw?