Companies that build themselves on selling open source software put themselves in the position where anyone else can copy them and compete with them on price, and price alone. This is clearly the disadvantage of open source. It brings plenty of advantages, which is why people do it - but you can't have only the advantages and no disadvantages of open source.

Open sourcing your product is a risky investment, and as with all risky investments, it might pay out, or it might not.