ASF communities work hard to be open to contributions from any and all parties, which is important for avoiding alienation of minority factions and keeping the community from fragmenting, and also for maintaining project independence and not getting captured by a single dominant entity. As a side effect, contributions are often negotiated but rarely rejected, which exerts pressure in the direction of feature bloat: the acute needs of the contributor tend to outweigh the diffuse benefit of simplicity.
Such pressure is not impossible to resist, but it usually takes dedication and and superior negotiation skills from core maintainers. A modular architecture is also very helpful for accommodating contributors without compromising usability, which is why so many successful ASF projects use plugins.