why is RMD requirements required to be reported per account, whereas my brokerage says it can be aggregated?

[Vanessa A]

It can be aggregated if they are the same types of accounts from the same employers.  If you are asking this because of an error in TurboTax with each 1099-R, you can simply enter it per account as this is about the software calculation not an IRS form.  It will all be put together on form 5329. 

[Mike9241]

Different types of accounts have different RMD rules, which would make the programming more complex. For example, if you had an IRA and 401k for which you must take RMDs you can not short one and make up the shortfall by taking more from the other. 

so for each 1099-R, TurboTax is asking how much on line 1 is an RMD