A keyboard is a digital piano, it is digitized version of an analog instrument. Have you ever used an MPC? You cannot do anything with them unless you load samples into all your pads, very different than a keyboard with which you can sit down at and play. Almost all samples are taken form other people's music, in fact, most beat makers pride themselves on stealing work that falls under free use and hasn't been sample/stolen before.
If a rock band were to "sample" a 16 bar phrase they would promptly get a cease and desist order or a lawsuit, even if they did it from a hit decades old. You don't remember Led Zeppelin?
I am not going to deny it takes time and effort to make a beat, but the talent part is minimal at best, it takes a good ear and in Kanye's case, well secured licensing rights to old hits. If you start with a hit song, it makes it a lot easier to make a hit song.