[cirenehc]

Because in one case the target is the individual. The other case your data gets aggregated and sold as bulk in the form of ad impressions (tracking).

A better comparison would be, the gov uses your census data to mail you flyers.

[staticassertion]

YEah I stalk a TON of people so it's fine, it's just aggregate stalking.

[loveistheanswer]

No, there is plenty of stalking/tracking which targets individuals. It's called microtargeting.