Yes but there is an expectation that the government doesn't tail you at all times for your entire life with no warrant, right? Largely because in the past it was infeasible for the government to do so: it cost too much money and required too much manpower.
That's what Alito was arguing in Jones: people expect to be tailed sometimes but they don't expect to be tailed at all times for a whole month. And commentary suggests the Court would have had a similar opinion if they had not sidestepped the issue by leaning on trespass.
As Alito said, the question the Court has not decided (and didn't need to decide in that case) is where the line is drawn. When does tracking a vehicle become a search and enter 4th amendment territory and require a warrant? (He said surely before 4 weeks.)