There's been discussions about dual-port expansion cards on the Framework forums[0], but the problem is finding a chip that will pass through all the things you expect USB-C to handle over both ports. This is actually a larger problem with USB-C, as each altmode is basically a different spec that reuses the same connector, with lots of negotiation and custom electrical requirements involved. So any moderately niche application will either require custom silicon or have absurd limitations.

You could obviously wire up an off-the-shelf USB3 hub controller in such a way as to get two USB3 Type-C ports in an expansion card. (I don't think two type-As would fit.) However, you won't be able to charge the laptop, use external displays, or connect external GPUs through either of the ports... which is kind of the expectation that people have with Type-C ports. If they sold such an expansion card, there would probably be plenty of people angry that they can't just have this one card for charging and dongles, and then fill their other bays with storage drives.

Related example: fiber-optic Type-C cables for long-run use basically only come in two flavors, DP and Thunderbolt. And the source device has to use that one specific altmode; there is no downgrading to USB 3 or 2.

[0] https://community.frame.work/t/dual-usb-c-expansion-card-moc...