Then why would he give his Bitcoin to coinbase ?  nostr.fmt.wiz.biz 

 Like people that do the same, they believe that they are looking after it for them. 

Technically, the relationship of coinbase to every customer is debtor and creditor.  

 That doesn't make sense .. if mstr already have 250 k btc in its custody ..why would Saylor give his coins to coinbase ..why not to mstr ?  

 MSTR are custodying with coinbase also