In T20I there is an apparent trend of team losing more wickets while batting first. Perhaps this might be one of the reason for them to field first after winning the toss. Currently(Oct onward) there are few series played across the globe, and on average teams are losing 7 wickets while batting first with average team score of 150!.
Pattern for losing more wickets – Teams like Afghanistan, England New Zealand South Africa, Sri Lanka, West Indies and Zimbabwe are losing more wickets while batting first.
Pattern of scoring more runs – Teams like Australia, Bangladesh, India, and Ireland have increased their average teams score while batting first.
Below Info graph displays years-wise 1st Batting performance for every team since T20I inception in 2005. All data updated at end of 2nd T20I between Pakistan v/ s New Zealand – 2nd Nov 2018.