Because the problem you are having with a seller may be a one-off, or not actually a scam, or out of the seller's hands.
Open a Dispute and get your refund.
Leave calm and factual feedback if you want to.
If a Seller loses too many Disputes, eBay will restrict the account at first in the number and value of listings they can make and if poor service continues, closing the account completely.
Listings that appear to be scams can be Reported without any transaction. EBay does pay attention to these Reports, as we can see from the many complaints from (usually) newbies who paid for the 'too good to be true' Thing just before eBay shut the scammer down.