Toncoin is not a TON-jetton; it’s a native currency on the TON blockchain, while jettons are smart contracts that respect a standard. Therefore, the direct exchange of Toncoin for jettons, although technically possible, is not optimal; it’s better to keep the gas payment and the amount sent separate. If we create a pair with a Toncoin and try to swap 1 Toncoin for a jetton, this 1 Toncoin will be also used to pay network fees, and the final swap cost may be higher than you expect. Conversely, when using a wrapped asset, you can be sure that you aren’t paying a network fee from it, making the swap easier and cheaper. Also, some DEXs only allow Toncoin-to-jetton pairs, and each jetton-to-jetton exchange is conducted via two trading pairs (jetton A to Toncoin, and Toncoin to jetton B): this increases trading fees and slippage (which means you risk buying an asset at a higher rate than you expect).
Thus, using a wrapped Toncoin is an optimal and more versatile option, since it is made to be more generic, and this provides more trading and other possibilities even initially.