creating is story is not that simple... even for a page a day....
and sometime it's better to end thing on a good note rather than forcing it to go on....
while it technically can still continue with random stuff...
it would probably feel more lackluster than the previous chapter to some... doing random stuff...
and well... doing that would... make it easier to do some slip up and fuck something later on...
on another note, if the story can, and would still be able to be developed more...
even if the author choose to end this now, the author can later choose to adapt a sequel to it... there are cases to this... (if the proposal/draft or whatever it's called got lucky to be accepted by the publisher side, that or make something like a doujin...)
I mean... there's seems to be cases where other manga do something like that... (doing random stuff after main plot)
it's not really a problem by itself since ultimately it's up to the author to end thing when it's time... that or the publisher start throwing the axe due to popularity problem or something else entirely...