If you go to a grocery store today to buy grapes, there's a good chance that the only type of grape you can buy is seedless. Nearly all grapevines in production today produce seedless grapes.
It turns out that most fruits today do not come from seeds. They come from cuttings instead. This is true of grapes, blueberries, apples, and cherries — pretty much all fruits except citrus, although scientists are working on that, too. A piece of a vine or branch is cut off, dipped in rooting hormone and then placed in moist dirt so that roots and leaves form. Because they come from cuttings, new grape vines are essentially clones of the vine they were cut from.
Seedless grapes actually do contain seeds at some point. But a genetic error prevents the seeds from forming hard outer coats like normal seeds do.