Not everyone NEEDS a gain antenna. A unity gain (zero gain) antenna is what is supplied with just about every scanner and HT manufacturer. May not be ideal, but they work, especially if you're within a relatively short distance of the transmitter antenna site. Gain antennas provide an advantage in weak, fringe signal locations.
It's no different than if you are receiving OTA TV broadcasts. If you're in the city, an indoor ant (anyone remember rabbit ears?) works fine. But if you're out in the country, 50 miles away from the TV towers, you'll need a yagi, pointed toward the transmitter. The more elements; the more gain, and the more directional if becomes.