If 4-6 airlines decided to start at your first choice base what makes you say that you can't start there as well? I don't think there is a limit on the number of airlines allowed to base at an airport. Everyone has the same chance to make it. If you move to your first or second choice base later in the game to properly get "started" you have deal with competing against the mostly well established airlines at that base, trying to find aircraft and waiting years for new aircraft, dealing with low CI, RI, ect.... You end up in a less favourable position than you would be if you started and stuck with the base you picked first day.
If you made a mistake with strategy than this is more understandable.
Well, speaking just for myself, I wanted a specific base and to run a specific airline type, so I could compare notes from a previous game based there, given the changes made to the game in MT#7. Two folk were already based there, it had 4-5 slots per hour at start of world : so basing there as well then would have been pretty pointless: so I messed about elsewhere and ran a few trials to see how the changes seemed to be working. Which was pretty useful, actually, and when the base became free, I moved in and now am pretty well established, running my little-bird outfit and, again, learning heaps about how the pricing model now works.
Of course, you are right in that if I had wanted a more popular base, then starting in soonest and regardless of day one competition would have been the sensible option.