There is always a need for elders and ministerial servants. At the District Convention and during the visit of the Circuit Overseer they stress over-and-over that brothers need to "reach out" for more responsibilities. They discourage that mindset when it comes to secular employment, but when it comes to the Organization you are viewed as spiritually weak if you do not get appointed as an elder or ministerial servant. The WTBS constantly pushed brothers to take on more responsibilities - volunteer for work at the District Convention, help with the Regional Building Work, or assist with the Hospital Liaison Committee.
It is true that appointments of elders and ms's all depends on how the elders of a particular congregation views a brother. Some are appointed simply because they are well liked - and when the announcement is made that brother So-in-So is now an MS or and elder most are wondering how that happened. Some elder bodies are overly strict of whom they recommend a brother to be an elder - a brother has to be super-super-super "spiritual" and be way old enough in age to be viewed as a "proper" elder.
Most elders that are deleted from their position is due to their family. Most of the deletions result from children getting into trouble - getting involved with immorality, drugs, or wanting to not be a JW anymore. Others are being deleted due to their wives - some wives become spiritually weak - not attending meetings regularly, not reporting any field service for an entire month, and in extreme cases getting involved in immoral conduct with someone in the congregation or with a non-witness at work. If an elder can't take care of his family - how could he handle a congregation.