'The market' is a handful of powerful miners anyway. As if your 1 vote could do anything about some fork abandonment or whatever. Also, do you monitor the whole network constantly? You have to sleep at some point. You know who does constantly monitor the flow of currency to a somewhat trustworthy degree? Banks and governments do.
In practice, this does not seem like a large problem.
The quantity is irrelevant, the exchange rate that reaches equilibrium is what is relevant
[1] There are marginal second order effects with human psychology (people feeling like they got more of something)/ brokerage arrangements (1 share being the smallest divisible portion of ownership that a SE will clear causing share subdivisions needed to be cleared by a broker)
If a company simply turned each share into two shares, then the market cap would be the same but the fractions of the markteshare that can be traded are smaller.
If the company suddenly issued the entire stock on the market again, the price would plummet to half.