Why there's no classical time control rating in chess.com?

No, it's not easy to add. The sizes of the site databases makes adding additional rating pools non-trivial. Then code and assets need added to support new pools in a lot of different site features, which is also a lot of work, but it requires the database to have the appropriate fields/tables to support it first.

I see, But I still feel like adding Classical would be beneficial.

Thank you nonetheless, I'm not a programmer.

I think that the current prices charged for the various membership levels are very reasonable for the quality of the site's features and the amount of usage so many of us get from chess.com in terms of hours spent on the platform per year, and that they could conceivably be raised slightly to support the additional infrastructure costs (servers?) and developer's time it would take to add a classical rating pool as well as the other features that are periodically added. In particular the friends and family plan is a very good deal when paid in an annual lump sum to cover six people, which breaks down to $2.78 per person per month, and I know my family gets a lot of enjoyment and usage out of this plan.

I think it's funny that small player base is the reason that classical has no time control because when you think about it, of course it won't have a player base if it's gonna be logged as Rapid anyways. Not to compare but Lichess has a functional classical system that people actually play because it exists. Or at least, that's how it seems to me. Maybe there are nuances I'm unaware of but this seems pretty obvious at first glance.