In our day-to-day lives during this era, there are times when social distancing isn't possible or practical, but the goal is to practice it whenever possible. With air travel you can successfully social distance in many aspects including through security, in the lounge, at the gate, boarding, deplaning, etc. Similar to at the grocery store, you may need to be closer to someone when passing them in the aisle. But just because that best practice can't be accomplished 100% of the time doesn't invalidate every other restriction that minimizes risk for all.

Think of it this way. If I can count on people following the published rules for an airline, then I can evaluate my individual risk tolerance for that particular situation. It's my personal choice to be on a plane given those risks. However, if people are not following the guidelines, and I discover that when I'm already trapped a confined space for multiple hours, then my personal decision about the risk I feel comfortable with has been invalidated by someone else's behavior.