The goal is to buy the largest percentage of the company with as little money as possible.
If the asks in an order book are (price, quantity) pairs of (p0, q0), (p1, q1), etc. with p0 < p1 < ... and you have $C in capital, then ignoring the "driving price of a stock higher" effect(i.e. if C/p0 < q0) you could buy floor(C/p0) shares.
However, if you purchase more than q0 shares, those will be priced at p1, p2, etc. and you'll instead buy C/(weighted_average([p0, p1, ...], [q0, q1, ... q_remainder]) shares(where the weights are the quantities). And because p0 < p1 < p2 ..., this will be fewer shares than C/p0.
At the extreme end, if you try to "clear out the order book", a stock that is nominally $10 you'd be paying $1 million per share to someone that put in a joke order to sell. So you'd be getting 100,000x fewer shares per marginal capital deployed compared to a smaller investor.
Also why are you calling his actions naive ? He made money as did others.