When the day just seems to fly by, networking takes last place on our list of priorities. It seems like wasted time, just to spend time "visiting" with people or asking about things that don't seem important to our needs at the moment.
Remember the Urgent/Important matrix? You have four types of activities: urgent but not important (the phone rings, someone walks in to your office), urgent and important (the building is on fire, your best client is missing a shipment), not urgent but important (planning, goal-setting), and not urgent and not important (rearranging the books on your shelves). Generally accepted time management wisdom says spend more time in not urgent but important in order to spend less time in urgent and important.
The problem is that while networking is important, it's generally not urgent. It's not like missing that Chamber mixer is going to cause an immediate negative effect. So it's much easier to spend more time in the urgent and important task of actual selling - especially if you're short on your quota at the end of the month. But again, more time spent in not urgent but important, i.e. networking, builds relationships to help bring in more sales, requiring less time in the urgent and important activity of getting one more sale.