I'm not sure which of those (if any) demonstrate conclusively that the computation had quantum speedup. I know experts have disputed at least some of the claimed demonstrations.

But how is it increasing? E.g., is there a Moore's law of qubits?

1998: First computers with 2 and then 3 bits of memory.

2000: Computers with 5 and 7 bits of memory.

2006: 12 bits of memory

2011: 14 bits

2017: 17 bits

There is too little data to suggest anything else than a linear fit. But then again, the early stages of exponential, or logarithmic, growth can look linear. We should wait 10-20 years to get more data.

    2017 - 17 qbits
    2011 - 14 qbits
    2006 - 12 qbits
    2000 - 7  qbits

Looks like a line to me. I expected something way more noisy.