IIRC Xbox had been criticized for quite a while at that point for having very few exclusive/first-party games worth buying an Xbox for. I always assumed this move was to try and fix that problem.
The (an?) incoherency with that is that this was happening at the same time as the ‘everything’s an Xbox’ strategy that saw them produce games for other platforms too.
That was a side effect from ABK acquisition, they bought studios that traditionally were cross platform, the year long acquisition discussion always promised not to touch them in that regard.
So you end up with this schizophrenic way that XBox became more of a publisher than a console brand, with a leadership used to cross platform (Sarah Bond), thus ‘everything’s an Xbox’ pivot for the "curve must always go up".