Bitcoin has way more branding power than Satoshis. If Bitcoin increases its value, we will reach a point where adoption will be blocked by the general perception that Bitcoin is too expensive.

Also, but correct me if I am wrong, Bitcoins are comparable to shares of a company. The whole Bitcoin network is controlled by the total number of Bitcoins. If you don't have Bitcoins and need to transact in Bitcoin, you need to buy some and become "shareholder", even if this is for the fraction of time you need to complete the transaction. Expanding the number of Bitcoins would mean open the network to new users and avoid having a centralized control.