The rumour at the time was that Google fully intended to enter the hardware business. they wanted to keep Motorola forever and didn't just buy them for patents, but Samsung threw a hissy fit and threatened to drop android entirely if Google was going to compete with them directly. Moto was sold as part of a deal with samsung (samsung intro'd a tablet with a very microsoft-y UI shortly before google sold motorola, and after the sale the software was re-done to be much closer to stock android)
Presumably, with the Pixel line going head-to-head with the Galaxy S last year the situation has changed enough that Google no longer fears that Samsung will ditch Android. It's also worth noting that the rumour here is that Google will buy specific manufacturing and hardware assets from HTC, but will not buy the brand. So it's less of a "buying the company and keeping the parts they want" situation, and more of a "buy only the parts they want" situation.
Presumably, with the Pixel line going head-to-head with the Galaxy S last year the situation has changed enough that Google no longer fears that Samsung will ditch Android. It's also worth noting that the rumour here is that Google will buy specific manufacturing and hardware assets from HTC, but will not buy the brand. So it's less of a "buying the company and keeping the parts they want" situation, and more of a "buy only the parts they want" situation.