Who, as an investor, would put 20% down for an investment property?
Historically (prior to early 2000’s), investment property required at least 20% down. In fact often it was 25% or 30% down payment required.
Also, to get the best terms (lower rates, no PMI) requires at least 20% down. Better loan terms means better cash flow.
Most real long-term, buy-and-hold investors put at least 20% down. Those who put down less would likely include flippers and speculators.