It's not just privacy that appealing about Grin, it's designed to scale based on usage. Grin is designed so that its network doesn’t get dragged to a standstill when transaction volume increases. This was the core issue in the Bitcoin block-size debate: there were more transactions than could fit into a 1Mb block. As long as there’s a restrictive block size limit, there will be a capacity issue. A dirty little secret is that to get around scalability issues, almost all payment processors and exchanges do off-chain transactions. Which begs the question: why bother using a cryptocurrency with blockchain? It’s a slippery slope. Increasing usage will of course increase transaction volume. To ensure that a block size can continue to accommodate volume increases, you have to streamlining each block by trimming transactions. MimbleWimble/Grin maintains that if an output spends an input, you no longer have to keep them because they cancel each other out. This greatly cuts down the amount of data you have to store and process. The only data that nodes keep is unspent outputs and block headers. Instead of thinking of blockchain capacity in terms of number of transactions, MimbleWimble/Grin is designed to grow with the number of users using cut-through. The streamlined blocks make growth sustainable over time as the transaction data set does not continue to get bigger. This increases privacy since transaction data gets removed and it also enables fungibility. That's the scalability answer Grin brings, in addition to privacy by default.