Reason for exhaustion in road trips

Travelling via 4 wheelers on road trips is something we all fancy. Long distance trips is the reason i have got a car, but the long distance drive gets me exhausted so i always wondered what could be exact reason for the exhaustion, for instance i recently drove in XUV700 albeit for 400kms but I didn’t feel it that much exhausting compared to my i20 which i have driven for 600kms at a stretch. Coming to the question what causes the exhaustion, is it the suspension, the seats, the different profile tyres or the space?