Because he felt his days were numbered.
They're practically non existent.
None, because they keep on asking why all of the other light bulbs in the house aren't being changed at the same time.
It's days were numbered!
February... because it has the least number of days
It makes them feel popular.
Because the Doctor can never see him.
One's a prime number, the other's a prime minister.
Because 7 8 9!
A calendar has a future...
I am dismayed!"