The challenge with a single tool is that it cannot meet most people's needs without becoming overly feature-laden. By assembling small pieces loosely joined, based on open standards, everyone can have something that works for their particular circumstances.

There are some tools that integrate these pieces, but most are proprietary and have user fees. My current system is free. If an organisation wanted to make a suite of tools available, then a multi-purpose single tool may be more appropriate, but I would not jump to that conclusion without some analysis.