Tubes these days are fired incorrectly so there are contaminants caused by the getter being under or over-fired.
Cathode structures are not being built with proper care. Contaminates get introduced, causing grid contamination during the operation of the tube and also causing arcing as the cathode coating flakes off the cathode.
There is a new US manufacturer of tubes in Carson City, NV that was showing at THE Show just last month. They are starting with a new 6L6 and expect to have a KT88, 2A3, 300b, 6SN7, 12A-series. They seem to be well funded. RCH Labs. The 6L6s they had on display looked quite nice :)