nodeは立ち上がりが軽くて速くてスケール時に使い捨てしやすいからだろう。

AWS Lambda Cold Start Language Comparisons, 2019 edition ☃
https://levelup.gitconnected.com/aws-lambda-cold-start-language-comparisons-2019-edition-%EF%B8%8F-1946d32a0244

https://miro.medium.com/max/3000/1*9sCYX6qNP2_v4h65dAXldQ.png
https://miro.medium.com/max/2100/1*yRoptbhiLIc8pcSkhKAWmA.png
https://miro.medium.com/max/3000/1*CTR45urzK4_gz177XyyWew.png

.NET遅っそｗｗｗ重っもｗｗｗｗ
Java遅っそｗｗｗ重っもｗｗｗｗ