Reason is optimum gain plus a combination of regulations. Actually this has had been a trick question for generations from 1960's onwards. Typically gain for vertical polarization is "more easily attained" in 88 to 108 MHz. Before the decade of 50's experimentation also revealed that for

1. For Mobile stations, such as radios and cars etc where vertical narrower beam is used to talk to end user gives better results.

2. For TV sets, that are primarily stationary, and receiving antenna's are pretty giant compared to normal FM hand held radios, you can afford to have horizontal polarization.

For more details, you can study : Integrated Circuits for Wireless Communications. Focus in the portion where it states Super Hetrodyne ICs and Power Amps. You would know how for TV transmission range it is best if we use circuitry horizontally polarizing the wave form. It saves a lot of Moolaaaah. :)