Shareholder Loans vs. Normal Sponsor Equity in LBOs

What exactly is the difference between shareholder loans and normal sponsor equity? From what I've read in the guides, shareholder loans generate tax savings (since they almost always have PIK interest which is tax-deductible), but are still treated as equity and exit calculations for IRR remain the same. It seems to me that shareholder loans are essentially the same as normal sponsor equity (both have the upside that comes with equity) but offer tax savings - so why don't PE firms use as much shareholder loans for LBOs? I'm pretty sure I'm missing something here, so any help is greatly appreciated.