Bands on Bandcamp usually pay more for their equipment and concerts than they earn from it. Those tiny independent bands are the most honest bunch of musicians you can find who do music by themselves and for the sake of music -- not for the sole purpose of generating revenue. There are people in there who rehearse in their own basements and who pay with the own money for recording sessions just for you to be able to listen to it.
You can listen to whole songs on Bandcamp because they want you to hear their music and they want you to enjoy it. That is the most important aspect (in contrast to these money-making, oppressive, DMCA-take-down-wielding music giants). If you don't like it, move on with your life. But if you like their music, consider tossing them a few dollars. It's a better investment than anything else related to buying music.
