When XP came out, it was a marked improvement over 98SE, not to mention ME. It was based on the highly advanced NT platform, which was far more stable under load than the consumer kernel previous home user iterations were based on. It wasn't limited to 1 GB of ram, or FAT32 and 137 GB hard drives. It sold great, and became the dominant OS inside two years as hardware outstripped the capabilities of 98. When Windows 7 came out, it was a marked improvement over XP, with far greater utility in a multi-core 64-bit environment that XP simply doesn't function in, it replaced it as the dominant OS inside two years as hardware outstripped the capabilities of XP entirely. Vista sold like shit, it was far more advanced, but hardware wasn't, so all it came with was poor overhead. 8 sold like shit too, for different reasons, a horrid gui instead of poor performance, but the lack of advancement was the same, and 7 still isn't failing to deliver on modern hardware.
They're essentially looking at a market purely driven by packaged sales, and performance gamers, anyone that puts their own together has absolutely no reason to buy a new OS unless they're playing DX12 games on it.
Your internet browsing isn't worth nearly enough to make up the cost of a free OS, what they're doing is giving you one you don't need for free and probably wouldn't have bought anyway, so you'll buy your next machine with Windows 10 having gotten used to it. It's the same reason they wont put DX12 onto the old operating systems, they need it to sell the new one because there is literally no point in upgrading from 7. XP plateaued near 80% market share, 7, even with it's huge advantages, around 55%, and unless they can get people off of it without anywhere near the same reason to switch performance wise, 10 will do even worse. XP obliterated every predecessor, and Microsoft would kill for that kind of success again, but their obstruction is their own damned product.