2.3.3 The ball shall be made of celluloid or similar plastics material and shall be white or orange, and matt.
Then why do amateur low level tournaments also use plastic ?
Not exactly because they care so much about the environment but because most amatuers want to live in fantasyland & use what the pros use.
I know of a state championship in USA that always used celluloid balls as official ball after 2014.
And for other tournaments they gave the option to two (or four) players involved in each match, a choice of celluloid or plastic ( I heard almost all of them chose celluloid).
BTW Adham Sharara did the same thing initially with 38 mm ball to pass the 40 mm ball after the first attempt to pass 40 mm ball failed giving this option as a peace offering (by promising to keep teh 38 mm ball also legal. It was for a while it seems and I do not know when it was removed from ITTF rules & which AGM or EGM approved removing the 38 mm ball, since this is a "rule" change & requires approval by 75% of general council of 228 nations of ITTF at an AGM or EGM)
Of course the Maximum allowed Pip Aspect Ratio reduction (from 1.3 to 1.1) failed as rule change in 1995 BGM & was passed as a regualation in Durban in 1998 by a closest possible margin of two votes (something like 19-17). The same strategy was also used by ITTF to pass with the Pip Density Reduction change by passing it as a Regulation of 2003 (How many members of even the ITTF's executive council, let alone the general council of ITTF and general playing population even know what this Pip Denisty Reduction regulation is, let alone its enormous ramifications in the aftermath of 1998 Durban change & 40 ball change of 2000 & the 40+ change of 2013 after 2003)