The scalability of quantum computing tech is a major concern but no one is claiming that it'll be miniaturize to that extent nor that this is even a goal.
If computational tech cannot be miniaturized then it is dead, as only at massive production quotas does the technology become useful enough to become inexpensive. This is exactly what happened with normal (non quantum) computers. Imagine if computers were still the size of a room... Terrifying thought
You're right that it does need to be miniturized to some extent but there's absolutely no need for it to be desktop sized. If in the future a quantum computer is built, taking up multiple rooms is not an issue at all.
The value is in a quantum computer existing at all, not it's availablity to consumers.
