Why do you think its so difficult and expensive to attain? What do you think institutional borrow costs are? And I'm not talking about Interactive Brokers... I'd wager that most funds are long biased because its more difficult to generate short alpha - not because of the costs of portfolio construction.
For the vast majority of symbols, stock borrow is cheap at institutional size.
Stock borrow costs vary from symbol to symbol. The ones you want tend to be the ones you pay for. Moreover, cheap doesn't mean free. Shorting half of one's portfolio is rancidity expensive compared to buying some puts. Even that is pretty expensive for total hedging purposes.
At the end of the day, most long-short funds are not market neutral. The ones that are operate on minuscule time horizons, and are better categorized as shadow market makers than funds. (Both in their operation and fundraising mechanics, the short-term traders tending to be more likely to deploy permanent--versus limited--capital.)
Delta neutral. And this is very difficult (and expensive) to attain in real life. Most funds are long biased because it's cheaper to be long than short.