It's just dry air causing shrinkage. Your house is not that air tight. Cold dry air is getting in and drying up the humidity inside. Increase the humidity inside to balance it out.

Your humidity level is too low in the home.

Seasonal movement with humidity changes. You are lucky they apparently laid the floor when the humidity was high otherwide the boards would swell and cup or buckle up in the summer. One of the many reasons wide floor boards are a bad idea. Also why gluing solid hardwood down is a bad idea. In a traditional installation you'd nail the floor with flooring nails that have a little give to them, and leave expansion joints around the edges so that it could expand and contract as a unit.

Your best bet at this point is to add a whole house humidifier to keep your rwinter humidity at 40-50%.

Were I a betting man, I'd wager that this was your first time with a white floor and wider planks. If you're up north where the humidity is low, this is a common and predictable occurrence.

Thank you all. @Timothy Winzell, this is my first time with light floors, but my previous home used the same width planks. I do live up north and the floors were installed in the summer, lol. Im glad to hear that my concerns with the floor are not a result of shoddy workmanship.

LOL. At least I was half right. The reason I guessed that was because many people have experience with narrower floors, which only have gaps about half as wide since they're distributed across more joints, and in addition they're held down by more fasteners.