1997 Kennedy Half Dollar

I notice that as well. Some of the 1996D are like that too.

Don't they use new dies every year? I seem to recall that dies are not good for more then 1 million strikes.

Dies can last for a few hundred thousand strikes so the 1997D run probably used 75-150 dies for a mintage of almost 20 million. As to why your Denvers look better than the Phillys, all I can say is that halves tend not to circulate much so they don't sustain much wear and that in recent years the Denver coins seem to be "nicer" in general than Phillys.

One possibility is becase in 1997 the Denver mint die shop went into full operation and they were making all their own dies. Before that Philadelphia made the dies for both mints. This means there could be differences in how the di were finished, or in previous years the Denver dies could have been hubbed from working hubs which were not replaced as often, etc. It's like the earl S mint morgans. All the dies came from Philadelphia, but they were polished differently and replaced more frequently at the S mint resulting in a lot more high luster PL type coins.