[frostmatthew]

Restaurants typically have fairly low profit margins, so there generally isn't a strong desire to spend limited free cash flow to upgrade/replace a point-of-sale system that's functioning satisfactorily.

Especially since it's not something capable of a significant ROI since the PoS system usually has little-to-no impact on either revenue or profit. A slow one could impact productivity - but this is rarely a bottleneck so in most cases there would be little gained by spending money to upgrade to a newer system.