"Up To" is a weasel word/expression. It doesn't actually mean anything, or at least nothing useful to the consumer. It means marketing can claim pretty much whatever they like. I can have a store with thousands of items, with a single item that is 90% off, and I can truthfully say that my products are "up to 90% off." A carrier can offer terrible data speed accept for a customer standing right next to one of their towers and marketing can still truthfully say "up to 20 Gbps." It's only meaningful/useful if it's "At Least..." instead of "Up To..."
But then a competitor would only have to find one place, anywhere, just on the outer edge of a carrier's range, where the data connection is intermittent, dipping under 20 Gbps, then the competitor could show that the carrier does not offer at least 20 Gbps.