1) Much hospital equipment is leased, it makes more sense to lease new bang up to date equipment in a new location than to move and recalibrate / refurbish old. The leasing companies tend to write off the old equipment as it's often not re-leasable / saleable. Arguably it could go to countries less fortunate, but again there's big transport / calibration / installation costs, and the issue of training in use, diagnostics & maintenance involved. Pretty much everything is done on a cost / benefit basis so if it's financially and technologically viable to move equipment they will.
2) Equipment left behind is often plain obsolete or now sub-standard, even if it looks interesting and in good condition (as you would expect it to!). Both technology and best practice change and evolve constantly.
3) Future proofing. State of the art modern hospitals want to start from a place of being bang up to date and cutting edge, not putting in ageing and old technology/machinery, in fact we as the public expect it. I'm sure you would be equally outraged if your sparkling new local hospital was discovered to be using sub-standard or old technology and not doing the best they could right?
But then it's easy to find something to be outraged about on the internet. It's not like you have to do anything about it other than press a few keys.