Unless it's properly glued then it will definitely get worse - a toe guard and tape will help to strengthen it but to be honest I doubt you'll see the end of the season with the bat (assuming you bat for an average amount of time). As a rough guess by the time you've bought a toe guard, tape and fitted them you might be better off just buying a cheap bat to get you through the season.
As for how it got there, well willow is a natural product and as such each bat has it's own 'weak' spots. Some bats will last for a fair while others will crack the first time you hit a ball. Also, things such as the amount of preparation, oiling, how the bat is stored and even much you play in damp condition will play a part in determining the life of your bat.
Judging from what I can see in the photos your bat isn't the best in terms of quality of wood so from experience if it was going to crack anywhere then that would have been the area.