Re: Windows 10 iso file.
Microsoft wants to unify the windows experience, by having all of their customer base on the same operating system. This creates a unified experience for the customer, improves their brand image, and simplifies support.
Windows 10 is also the gift that keeps on giving (giving to Microsoft, that is) because it's a tool for marketing and data collection. Its telemetry services allow Microsoft to collect statistics that are worth a fortune to advertisers.
Also, there's no reason to charge money for the iso file. You have to pay for a license key anyway.