The PS5 didn't have enough stock to beat the PS4's initial holiday sales, Sony confirms.

Demand for Sony's next-gen PlayStation 5 has far exceeded supply, and limited availability has hampered console sales. Sony reveals the PS5 has only been able to match the PS4 during a year of unprecedented sales potential.
In Q3'20, which stretched from October through December 2020, the PS5 sold-in 4.5 million units--the same sales volume as the PS4 during its holiday 2013 launch. The numbers are actually pretty good as the PS4 was no slouch at launch, but Sony could've hit much greater thresholds if production and console stock hadn't been so restricted.

Sony says it is confident the PS5 will surpass the PS4's initial six-month sales and beat the 7.6 million shipment mark.
"We are currently on track to meet our sales goal for the fiscal year of more than 7.6 million units, but we have not been able to fully meet the high level of demand from customers," Sony said in its Q3 financials.
"We continue to do everything in our power to ship as many units as possible to customers who are waiting for a PS5."
AMD, who supplies the chips for the PS5, says production will be tight until the second half of 2021. This will take a bite out of Sony's established sales targets.