Why do I have to push the gas pedal to the floor to get my car to start?

Most likely the reason is that an oxygen sensor is getting insensitive and causing the computer to think the engine needs more fuel on start-up.

When the weather conditions are slightly above freezing, cloudy, and moist, it aggravates the problem of a lazy oxygen sensor and can even cause the spark plugs to frost over and prohibit starting.  Letting the vehicle sit for about an hour and trying to start it again, is the recommended action.

When you put the gas pedal all the way to the floor and crank the engine, it puts the computer into a different program for starting.  The computer cuts back on the amount of fuel it is putting into the engine and allows any fuel in the engine to be flushed out.

This bypasses the learned response of the computer(thinking it needs more fuel), and allows you to start the engine on less fuel than it thinks it needs.

Get that oxygen sensor checked.  And while you are at it, check the condition of the spark plugs.