if you have 3 apples but you can't eat them because you have no teeth, that doesn't mean you have infinite supply of apples.

the important thing about bitcoin is that it has a cap and that cap means you can't ever have as much as you want or print as much as you want like you do with fiat (paper money).

additionally since you are comparing it with ethereum (although ETH is indeed unlimited), the distribution is important. for example compare the supply of bitcoin and ethereum. bitcoin is at 17 mil but ethereum is above 100 million.

same with gold, it is limited but you can't suddenly extract a million ton gold overnight. it takes time to find new supply and enter it in circulation.
for cryptocurrencies a good cap and a good distribution design with ensure the supply is produced and distributed properly and helps with the price rise but a bad design and no cap will end up like no cap coins that keep losing value.