The problem with this is that time zone definitions change, both in the future because of political and administrative changes, as well as in the past, when mistakes are corrected. So a datum like "1st of May 2022 6pm in London" is not a fixed time. And therefore, you can't do any useful computations with this, like what is the time interval between then and the current time, or is this timestamp before, the same, or after, "1st of May 2022 6pm in Madrid". You can't even compare timestamps in the same time zone, because on some days you don't know whether 2am != 3am. Without the ability to do computations or even basic comparisons, such a type wouldn't be very useful in a database.