@Delmana you may think it was a spontanous decision do decrease the number of ranks, but it was not, and especially on merging Commoner (Member) and Thrall (Droog) into one rank (Adventurer) more than one long lasting discussion was held (which are unfortunately gone due to the Forum Crash we had last year), but here the most important points:
Commoner and Thrall were merged to one rank with all the permissions the former Commoner had because this rank did not serve any purpose for the sake of building middle earth; The rank could be very easily attained and thus did not show off special building skills nor trustworthyness.
Foreman, Artisan and Steward were merged into one rank as all of these three more and more performed all of the main tasks of each of the three ranks (leading/setting up large projects, leading jobs, make concepts/build styles)
"Ranger" was changed to "Guide", "Bounder" to "Enforcer"; and for the merged ranks "Adventurer" and "Designer" were chosen, these were driven by the intention of making all rank names easily understandable to new members by being pretty self-explanatory. The change from Vala to Head Designer / Enforcer happened at a later point but had a similar idea behind it.