Oh but they tried that in the past -- those products had a consistent result of killing the whole market segment then themselves.
1. Windows CE PDAs -- almost completely replaced healthy PDA-oriented OS due to Windows name, then wiped out the first generation of non-phone PDAs due to being absolutely inadequate in all ways possible. Survivors were iPAQ (Windows CE/Mobile), Palm (PalmOS), Visor (PalmOS), Blackberry (Blackberry OS, a phone but from PDA generation).
2. Windows Mobile phones -- sold to carriers, disappointed users, lost all market to dumbphones and Symbian-based Nokia, then completely wiped out by iPhone.
3. Windows Phone phones -- Survive by being produced by zombified Nokia, can't get any presence on the market due to iPhone and Android competition.
4. Windows RT tablets -- No one bought them in the first place.