Cost reasons I'd assume. Tape drives are expensive and complicated. IMO, thats one of the reasons why HDV was designed to work w/the same physical components as DV (no need to R&D and build new tape mechanisms). AVCHD can achieve adequate quality at a very small file size and that coupled w/the expanding bang-for-you-buck of flash memory means camera makers probably see it as good time to start w/a "clean slate" and start weaning consumers off tape based cameras.
Er, I could be totally off here (I don't think I am though) but that's completely wrong. First, you can store digital data files on tape. People (me for one) do it all the time with tape back up systems for computers. Second, HDV camcorders record their video as MPEG2 files that can be pulled off the tape directly as .m2t files (MPEG2 transport files).
My best guesses as to why there's not any recorders like this is that the small(er) size of AVCHD video allows the use of other media, like flash and HDD, pretty effectively and so doing that gives them other options in design. Smaller, lighter, better battery efficiency, etc. Beyond that, there's probably consumer confusion to keep in mind (this camera records in X format, but onto the media that Y format uses, unlike all other X cameras), licensing issues with whoever controls the miniDV name/media/etc., and other things that I'm just not thinking of at the moment.