Access to New markets.
You will find that in the real world it is much easier to do business with or manage people that you have met in person. You can get to know people through remote communication but it takes more time and probably will never reach the same level. Humans are very effective at building relationships face to face, partly thanks to subconscious non-verbal communication mechanisms using gaze direction, blinks and other signals. Face-to-face meetings work best everywhere, but in cultures where relationships are especially important they are indispensable.
See with your own eyes.
Relying on digital communication and other people to inform you about what is happening somewhere far away is notoriously unreliable. It’s like exploring another country using an autonomous rover. You can get some information about what is happening in a remote office, trade show or customer through your phone, but it is no replacement for actually being there. The picture you get from the reports of other people is always selective. Personal observation also misses some things but it gives a better overall picture and lets you see things that you would never have thought to ask about.
Travel is motivational.
One of the most neglected reasons for sending employees on business trips is that, if done correctly, it can be very motivational. Most employees feel that the honor of being chosen to represent the organization and the stimulating experience of exploring new cultures to be very motivating. Many people also feel that their apparent status in both their organization and the community grows if they are sent to trade shows, conferences, customer visits and so on. This had to be done correctly, though, so flying proper airlines, staying in nice hotels and a decent budget for meals.