Open-source alternatives to popular B2B tools
Everytime I look into B2B software space (I am a complete outsider, btw), I see that here and there always pop up some new company, offering something similar to competitors and what can be stiched together using open source (and almost free, not counting the support) tools. How these companies thrive? Why customers keep buying new stuff, when there are solutions already to most of the business neeeds out there (and even free ones!). 
Is this still the case of idiot-managers doing decisions like "nobody was fired for buying IBM" (and now SAP, salesforce, ) or am I not seeing something? Genuine qustions, really interested.