This is because Windows is used by a huge amount of people. All hardware companies will want to be associated with Microsoft Windows because everyone will buy their products. You have to pay for most commercial software on Windows even though there are some free ones out there. Many software on Linux are available for free, for example they have Open Office and this is very similar to Microsoft Office but the only difference is that it is free. Linux may have a lot of support now with hardware, but that wasn't the case when Linux was in its early years. Linux doesn't yet have all the hardware support that Windows does