disks are wiped by random data to thwart some cryptanalyses
As you may know, SSDs never really erase data, they just mark the block and write on the next one. So, for the wiping to be effective, the whole disk must be rewritten. And even that “whole disk” is still not whole because of over-provisioning, i.e. even more writes may be necessary. All that is bad for SSD.
If the disk was encrypted, it is highly unlikely that anyone can recover data from it without the decryption key. Or at least I don’t know how that can happen. Plus, while you work you keep writing and writing new encrypted data in different places.
Does anybody know why Qubes writes so much?
By default logs and volatile volumes are written to persistent storage. Perhaps download cache during updates too. I don’t think that could easily result in 2TB of data writes though.
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You can also manually create a RAM-based pool and your AppVMs through CLI, specifying the volatile volume to be on the RAM pool.