One of my grandfathers worked for a telephone company before he passed. That man was an absolute pack rat, he wouldn’t throw anything away. So naturally he had boxes and boxes of punch cards in this basement. I guess they were being thrown out when his employer upgraded to machines that didn’t need punch cards, so he snagged those to use as note paper. I will say, they were great for taking notes. Nice sturdy card stock, and the perfect dimensions for making a shopping list or the like.
It’s likely CentOS 7.9, which was released in Nov. 2020 and shipped with kernel version 3.10.0-1160. It’s not completely ridiculous for a one year old POS systems to have a four year old OS. Design for those systems probably started a few years ago, when CentOS 7.9 was relatively recent. For an embedded system the bias would have been toward an established and mature OS, and CentOS 8.x was likely considered “too new” at the time they were speccing these systems. Remotely upgrading between major releases would not be advisable in an embedded system. The RHEL/CentOS in-place upgrade story is… not great. There was zero support for in-place upgrade until RHEL/CentOS 7, and it’s still considered “at your own risk” (source).