Take your analysis to the limit, and see if you still go with it.
There are now 1 million doors: one car and nine hundred ninety-nine thousand nine hundred and ninety-nine goats.
You will pick a door, then you will be shown 999,998 goats.
Finally you will be given a chance to swap your choice with the 999,999th door.
You reason that you know that 999,998 goats will be eliminated.
There are only two doors where the car can be - the one you choose and the 999,999th door.
So they both have 50% chance of winning.
So you choose a door, stick with your choice and expect to win 50% of the time.
Right?