HELOC limits are related to mortgage balances.
High mortgage balances = low HELOC limits.
The people who are buying homes at current prices, typically don't have much left (i.e. they may be at the full 80% of their loan-to-value, implying zero room available for lines of credit).
The only people with home equity to spend are typically those who have owned for more than 10 years. Not to mention, banks aren't as loose with credit as you imply (credit adjudication rules have gotten tighter).