The communication rating and auto-5 is actually one of the ones I understand, although it's a bit less relevant now since it can't result in a defect.
I think a lot of people misunderstand the parameters as eBay suggesting that communicating with buyers is bad, but that's not what it is about.
Think about the fact that for a long time, sellers complained about receiving low DSRs, about how it was unfair because they resulted from buyers who didn't realise just what it was meant to be for, or they (the sellers) were getting blamed for things that weren't in their control. The classic example of this was low ratings when postage was free, so eBay came up with set parameters where a seller could take this out of the buyer's hands (if the buyer pays $0 postage, it's an auto-5, if a buyer pays any amount of postage, then eBay won't rate the seller on the buyer's behalf).
Ok, so translate that to communication, in that eBay had to come up with certain parameters that would mean there was nothing about the transaction communication that the buyer would rightfully need to assess independently, and then also remember that there are a lot of different ways to communicate with someone, which means communication is not limited to a member sending another member a manual message.
The following things all communicate something to your buyer, all without sending them a direct message.
Title (and subtitle, if used)
Images
Item specifics, condition and description
Price
Payment options
Postage costs and any auto-discounts
Return policy and other TOS you may write
Handling time and ETA (though I realise a lot of sellers would rather eBay left that out, myself included, but because I know it's there and often unrealistic, I have a 2-day handling time when it's rare I don't post the same day).
Then there's the range of post-sale notifications that are auto-generated when you take certain actions - leaving feedback, marking an item as posted, uploading tracking where applicable.
Ever seller communicates with their buyer, manual messages are just one form of communication and it's not always necessary.
If your listing and post-sale processes have communicated all the information the buyer needed, eBay can assess this as an auto-5 on behalf of the buyer. If a seller does need to communicate outside of the above, then the buyer is the one privy to the additional communication, therefore the buyer needs to be the one to rate it, if they wish to.
eBay even go so far as to point out that they don't see communicating directly with buyers as a bad thing. The opportunity for an auto-5 is not there to discourage manual communication. At most, it's there to discourage it from being necessary.
