Okay, so what you're saying is that it's simply a preference, like what colour you prefer or what your favourite food is. That there's no actual objective reason to care?
There's probably an element of this in it but it also has at least 2 other components, at least for me:
As someone said earlier, I don't like bots assuming I will like "this thing X" just because I showed interest in "that thing Y" earlier. I've been online since 1995 and one of the joys of the early internet was just the completely random nature of what you stumbled across. I like to preserve at least some of this - it broadens my mind.
Secondly, whilst the storage of massive amounts of data on me by corporations or governments may be relatively benign at the moment, I can't help wondering how it could be used under slightly different scenarios.
Even with my efforts to maintain a low profile on-line, something really weird happened a couple of months ago.
My wife is the only senior executive in Europe for a listed US tech company. She appears on their webpage as being based in Switzerland. One euthsiastic analyst tried to generate a good "pump and dump" story by google search. He found the Swiss phone book where we are listed as Dr War and Mr Monger with our address and phone number available. A search of my name and address turned up the public records of the Swiss company register where the various Swiss companies that I have been a director of were listed. Based on this info, he published a speculative article suggesting that my wife's company was planning to do a big deal with a major Asian company in the same field purely because she lived with a former director of a few Swiss subsidiaries of this Asian company. He achieved his objective. The share price of the little tech company had a nice little blip as the day traders picked up on the article and the analyst would have made a decent profit.
What could google do with the data it stores?