You'd be surprised and with two printers in most machines the cost soon adds up.
But it's a rather essential part of running a railway. Almost as important as having trains and platforms!
I have never understood how things like the provision to give customers information on train running, or machines to sell tickets (and tickets that are readable) are somehow considered optional extras.
I know supermarket analogies rarely work, but let's imagine if a Tesco set up a new megastore and thought it only necessary to install 2 checkouts.
As it happens, I also think they should be upgrading TVMs from time to time - not just the software but the hardware too.
Newer TVMs from the same manufacturer are MUCH quicker to respond, making them quicker to use and reducing or even eliminating errors. Older ones chug along and play catch up, and when you make an error, it takes ages to correct or cancel and start over.