it's just because people feel a need to justify to strangers on the internet why they spent their money the way they did. they also feel as though they have to be on a "team" because they feel included in a bigger group.
it's gotten worse now too with all the sales info out there now a days, because people think that sales numbers actually matter to them as a general consumer. for as "terrible" as the x1 is selling (according to the internet) it's launch was better than the 360 launch was, regardless how it compared to the ps4, yet for some reason, people think it's failing.
sad really.
I follow the numbers weekly in the various markets.
The XB1 DID sell more than the 360 launch window.
However, it has rapidly dropped below the 360's monthly sales after that period, and is on track to cross streams fairly soon (probably before the end of the year, certainly no longer than next spring).
The 360 was initially
heavily supply constrained, and then their problems compounded by having to divert new units to be RROD replacements, so 'outselling 360' in the launch period is a pretty weak statistic honestly. The 360 took off after Gears came out and really moved the holdouts from OG Xbox and PS2 over.
None of this means that XB1 is guaranteed to be a failure, in all probability it's headed for a ~35M lifetime sales figure. I know of many consoles that sold MUCH less that I still love, so yeah sales aren't the end-all/be-all. One could argue that the monstrous sales of the PS2 led it to be supported for a lot longer than OG Xbox was supported, but if monstrous sales were all it took, where's Wii support been for the past few years? (yes, everyone knows that TONS of Wii sales were to people that will probably never buy another gaming console in their lives, and maybe never had before either).
There will be a 'round two' period where the majority of the sales of PS4 and XB1 will occur, and it's going to be the 2015-2017 period when both consoles are available around $300 or less, with multiple major franchises in place, no cross-gen mucking up the quality, and plenty of old PS3s/360s hitting the dustbins.
So, I love following the sales, I like examining PR spin, I love seeing the various strategies, failures, and successes of the major players. I like predicting and being correct. But none of that means that any particular console is GOOD or BAD for anyone.
The only thing that matters is if the owner of the console has fun and feels they got their money's worth out of it.