I don’t know why it’s only Enterprise, but you can leave feedback here.
Considering that it’s only in beta, it’s always possible that it might come to other plans in the future.
In the meantime, you can very easily setup this exact same functionality for free in Make.com. Simply setup a mailhook to receive incoming email messages, and then use the Parse CSV module to parse the contents of an attached CSV file.
It is common for beta features to be available at first to only Enterprise accounts. This lets Airtable control the size of the beta, as it is easier to deal with fewer users if any issues come up. This feature may remain an Enterprise only feature, or it could be later made available to other plans. Airtable has the right to make that pricing decision.