why do I have two OST files with constantly the same exact size?

I am using Microsoft Outlook 365 on Windows with multiple email mailboxes. One mailbox is a microsoft hosted mailbox with a custom domain name (lewins.email) and another is a gmail hosted mailbox (GSDVS.COM) which is accessed from inside Outlook using IMAP.

In my data files directory I have two OST files, one for each mailbox and they have almost exactly the same date/time stamp (which I guess is not strange since they are both being constantly updated by Outlook) but also the exact same size down to the byte. Why is that? Shouldnt the size be different? Isnt something wrong with how my outlook is setup?

Some screenshots below, feel free to ask if you need more info about how each mailbox is setup.

Thanks for any advice you can give.