They do! Well, at least some of them. There is for example a project called TAMDAR (Tropospheric Airborne Meteorological Data Reporting) that e.g. Icelandair is a part of. [There is a document published by the Icelandic Meteorological Office about it.][1]

Another example is [MOZAIC/IAGOS: Atmospheric Research Using Commercial Airliners][2].

  [1]: https://www.vedur.is/media/vedurstofan-utgafa-2017/VI_2017_002_rs.pdf
  [2]: http://www.fz-juelich.de/SharedDocs/Pressemitteilungen/UK/EN/2014/14-05-21IAGOS.html