The absence of the two side windows is not so much related to reentry concerns but simply to not being needed on this mission. The only reason there are two windows on either side of the hatch is that the window structures, like the rest of the structures, need to be flight-proven on this test mission.
Two windows are enough for that. So, why install four windows, on an unmanned spacecraft, when only two are actually needed. And remember: those windows aren't cheap given their complex multi-pane nature and all the associated seals.So, the weldment (pressure hull) was made with all four window openings, but the two side windows subsequently had pressure bearing plates installed in stead of the actual windows. On the inside a simple black cover plate was inserted in the window openings of the interior paneling. On the outside SPAM coated cover plates were installed in the backshell.
The manned Crew Dragons (from DM-2 forward) will have the full set of four windows so that the crews can enjoy the full view from orbit.