Perhaps the realtors you've dealt with have had bad experiences as buyer's agents. Most realtors of which I am aware (admittedly not a huge number) work as both buyer and seller agents.

If you are a serious buyer, I'd expect that a realtor would rather represent you than a seller (although as I said previously they'll likely still handle both sides). The buyer's and seller's agents split the commission, but the seller's agent might have additional costs in marketing the property. The buyer's agent is just out a bit of time and gas on their vehicle.