Specifically, VHS had both longer recording times and cheaper VCRs (due to Matsushita’s liberal licensing) than Betamax did. Beta only had slightly better picture quality if you were willing to sacrifice recording length per tape. Most Betamax users adopted the βII format which lowered picture quality to VHS levels in order to squeeze more recording time onto the tape. At that point Betamax’s only advantage was a slightly more compact cassette.
Also to correct another common myth, porn was widely available on both formats and was not the cause of VHS’s success over Betamax.