From a singular technology perspective, indeed it seems like investing a lot of money into a hypothetical device. However, there are many other factors you have

From a singular technology perspective, indeed it seems like investing a lot of money into a hypothetical device. However, there are many other factors you have to consider. 1. Quantum computing is a cryptographic arms race at the moment. One country can choose not the invest in it, but assuming QCs work, whichever country makes one first, is going to win big time. In a way, its a national security issue. Nobody wants to be left behind. Funding levels have to reflect this. 2. Many different architectures for QCs are being researched on, and in each area we have made tremendous advancements in new techniques of quantum-level-system control and new ways of nano scale manufacturing etc. The feedback alone from these advancements will enrich and enable many other areas of science and technology. For instance, the development of photonic quantum computation also advances the development of optical classical computer as the basic architecture is very similar. 3. Many physicists like myself don't care too much about actually building quantum computers, though it would be nice. Whether or not QCs are possible, just forcing ourselves to think about physical reality from a computational and information theoretic perspective has resulted in massive advancements in physics, a field which had pretty much stagnated since the 80s. The ideas generated from studying quantum information and computation have percolated into other areas of physics such as gravitation and the structure of spacetime. And its not sufficient to just think about QCs in the abstract. New ideas such as novel error correction codes are generated when physicists are forced to think about specific architectures and their limitations and/or real problems faced in the lab.