LordEntrails
Hero
The assumption in fifth edition is that you're playing without miniatures, not with them (see the PHB and DMG), so I don't think that explanation holds water.
Even running published content, the DM still has to think critically. Mistakes like these occur in published products all the time. Kudos to the OP for spotting this and pointing it out to those of us that aren't paying such close attention.
Just because the DMG says mini's are not needed etc, doesn't mean that the mindset of the designers doesn't account for the need for people to want to use battlemaps. Years of habit and the related assumptions are not broken without a conscious effort and need.
As has been said, as long as you use the maps with some critical thinking, adjusting and using other techniques as well, the maps work just fine.