To be fair, plenty of sufficiently old computers are so power hungry that they can be replaced with a modern device that pays its cost (even including many externalities) after only a brief period of operation.
The ones that are sufficiently different from modern platforms still need to be preserved.
You can argue that the real serious time is spent on the peripherals in order to read old media. I haven't seen a full list of formats for both computers and video tape (plus cards, paper tape, etc) but it has to be pretty big.