The difference in DNA replication rate between prokaryotes and eukaryotes is still under current research, but the basics are understood. It is very much a matter of complexity, as eukaryotes are more complex in many different ways. I found a very useful reference for this and other kinds of related questions. Briefly, some possible reasons:
[...] in eukaryotes, the DNA template is compacted by the way it winds
around proteins called histones. [...]
The DNA-sequence is not as easily accessible in eukaryotes, the unwrapping and re-wrapping of the DNA takes some time.
[...] The coordination of the protein complexes required for the steps of
replication and the speed at which replication must occur in order for
cells to divide are impressive, especially considering that enzymes
are also proofreading, which leaves very few errors behind. [...]
This underlines another rather important factor. The speed of the polymerases replicating DNA is very much related to their accuracy.
[...] This proofreading capability comes with some trade-offs: using an
error-correcting/more accurate polymerase requires time (the trade-off
is speed of replication) [...]
And just for completeness, here is a compete overview of DNA replication in the three big systems.