Why is it bad to video record at a store? Why do people even care?

Where you are in the world it might actually be illegal to record or photograph in a 'private place'. Although a store is open to the public, the owners of the store can control what activities take place in the store. 

Security and privacy reasons. If you record the layout of a store, you could use the footage to find weaknesses and plan a burglary. If someone is recorded and it's posted, it may be a problem for them or they may not like it.

A competitor may use the footage to gain an advantage. 

Because they feel it uncomfortable

Because most people are ugly and don’t want to be captured on video ya dumb fk

Depends on what your recording it for, i.e an incident at the store maybe that's ok but recording products is another thing

People and businesses get paranoid about what the purpose of the recording is.  If you want to record somewhere, just ask the store owner or manager first.

almost all stores will not allow you to record store displays. they care because how they go about marketing to the customer is not something they want to share with the competing businesses. they are also nervous because you might capture the images of their shoppers in the store and that could easily lead to a lawsuit. all stores have to be treated as private owned property and as a photographer you must respect the wishes of the owner. if you have a legitimate reason for photography, then get permission first and make sure any person in the shots have given model releases.

The bigger stores put a lot of time, effort and money into developing a style or a brand. Obviously they can't stop competitors coming into the store, but they don't have to make things easy for them.  It's not just a case of seeing what looks pretty - recording things like people's reactions and "dwell times" are valuable data.  

Because you're recording in someone else's property. They have every right to tell you not to. It's not your place, nor a public place.

Because there are security cameras at the ceiling