I think you do not understand how it works. Hardfork does not alter the maximum supply of bitcoin, it just creates an altcoin based on the current blockchain. But bitcoin will still have 21M maximum supply. If ever the hardforked coin survives, it is just an altcoin and will compete with bitcoin on the market.
Yes bitcoin really does not have limited supply. The argument is again and again that the value of Bitcoin will increase because supply is limited to 21 million. But this is quite simply wrong. Every time Bitcoin is forked that is in real terms an expansion of the Bitcoin currency beyond 21 million. To some degree the same is true of alternative crypto currencies which will flood the market. There is already more than 1000 cryptocurrencies . Bitcoin is really successful.