in 2009. without a market price. without a economic value. people still thought bitcoin was worthy(feature and benefits).
they were willing to use their time and electric to use bitcoin.

people were developing it and transacting between each other.
the economic value increased the more people seen the features and benefits. even before there was an economic value.

by the way you are not forced to but 1btc at $40k
you can if you wanted acquire 0.001 btc $40

no one is forcing you to hand over $40k in a lump
unlike shares where you can only buy whole shares. or stocks only in certain size allocations.

you can still use bitcoin even without paying $40k