TCM raises some interesting points regarding the membership numbers.
Bear in mind that ETO has been running for about 10 years, during that time there will have been people who have registered here and then:
Lost interest in ETO
Lost interest in electronics
Had changed circumstances, eg student starts work, gets a girlfriend, gets married etc
Never post a question or reply but are just happy to read the various goings on.
Post a question relating to a one-off problem, and then never return. That question may have been answered fully or maybe not replied to at all.
Some post a question and then never return to read the answer.
Some, post meaningless reples to existing threads (this seems to be quite a popular activity recently, is it the same lame brain registering several times with different user names?).
Some people may die.
I myself am a member of a couple of fora (?) where I regularly just read the goings on, but have never posted.
Overall I think that ETO is quite healthy.
JimB