Because his risk and return profiles are completely different from the DJIA. active equity managers don't generally outperform their benchmarks but it's at least appropriate to compare them to an equity based benchmark, other than the Dow which not only is just 30 stocks, it's equally weighted. The S&P and other indices are at least market cap weighted. Depending on the strategy or objective, a simple comparison to the benchmark may be enough to evaluate their performance, but managers often have mandates other than "beat the S&P" that fit investor needs which indicate their performance won't track the S&P - for example, you would expect a levered beta portfolio to outperform/underperform when the market is up/down. Low Beta mangers who approximate the S&P may actually be outperforming when you consider risk adjusted returns. Others seek to minimize tax impact. Multi-asset managers can't really be compared to an all-equity or all-fixed income benchmark, etc, etc.
The point is, it's hard enough for active liquid asset managers to be compared to a passive single asset class index. comparing Trump's business to them makes even less sense.
Edit: many active Fixed Income managers do outperform their benchmarks.