Not true. When I first started playing the idea of getting into six figures in A/D (100K) seemed fanciful. That was in the early days of KA when the level topped out at 50, and having 20-30K A/D was considered impressive. Don't believe me? Have a look e.g.
at this post from April 2012 from Ghost -- a strong player at the time. His stats were:
KA Ghost Level: 50
Attack: 12,178 Defense: 16,051 Income: 2570
Laughable by today's standards. I've seen people at level 16 with 200K A/D. The game has changed.
A year ago as I passed 100K and then 200K I saw folks up around 500K and could hardly believe it. The idea of hitting 1M in A/D seemed fanciful
. Now the guys in FUN are around 4-5 million, but a year from now that will look quaint as people will be hitting the 100 million (mark my words). So the only way the FUN guys, and anyone else at the top of the rankings, will remain untouchable is to keep pouring money into the game. I can guarantee that "coasting" based on currently having top units and top boosts will not cut it.
As for why they do it and whether it's "fun" to be unbeatable... Who knows? Some people like playing games in "God mode", others find it boring. Some people need to be the best, some are insecure in RL and find validation through on-line mastery... different stokes.