The Portfolios with low active share, need an extremely large outperformance from the active components to achieve the same outcome as compared to portfolios with a relatively higher active share.
To top it off, fund managers that run closet indexing or index hugging portfolios/strategies need to also account for asset management fees and dealing costs which eat away a good part of investor returns. Imagine a fund that mirrors the index to the extent of 70-80%, the return will likely mirror the index and then once deduct a 2.25% total expense ratio, underperformance is inevitable. Index hugging is a classic recipe for consistent underperformance.