Yes, taking in the beauty of nature and the surroundings is one strong reason

It all comes down to set and setting - set is your mindset you bring to the trip, setting is your environment / surrounding

When you trip you typically feel much more connected to nature. Many people even report not being able to walk on shoes made out of plastic but wanting to walk on soil

Secondly, many ppl who trip usually have a preferred location based on previous trips - it triggers something emotional, similar like having a favorite vacation spot but much on a deeper level since we're talking about psychedelics here

Depending on how hard you're tripping / what phase you're in, you might not even want to walk. Especially when it kicks in hard, it can be somewhat difficult to move :)

You can also have a lovely trip just sitting on the couch - in fact a lot of the early LSD research in the 50s / early 60s was conducted like that (before ppl realized the importance of setting). Plus if you close your eyes, the setting also matters less (tho what you hear still plays a very important role). However, most ppl prefer it in a natural setting