Floats are only marginally tied to the place where they appear in the LaTeX document; that place basically means "starting from here, try and find a suitable spot where the float can be typeset". The caption and the number are in fact thought for giving a description and defining a label for referencing the object.
According to Murphy's law “the place where I'd like the float to appear is never the one that will be eventually chosen”; this seems to be a joke, but it's really what happens in the majority of cases: particularly, if a float is large, the chances it can be placed at the “right spot” are small.
I'd add also that I find it dubious breaking an enumerated (or itemized) list with a float, because it hinders legibility more than if the float is at the top or bottom of the page with an appropriate reference in the text.
In general, LaTeX is not more reluctant to place floats in the middle of a list than in other places. But it respects the relevant parameters' values. A good place to look for information is Frank Mittelbach's answer to How to influence the position of float environments like figure and table in LaTeX?