They are. Pixels are also good for longevity and alternate ROM-s.
The problem is budget phones—people who can't afford to pay 600€ for a phone are left with devices that are obsolete in 2 years and no custom ROM-s even when the bootloader can be unlocked. The ROM community mostly consists of enthusiasts who are generally not interested in budget devices.
Case in point: my Poco X4 Pro. Excellent hardware (5G, 120Hz OLED, headphone out and SD card slot, IR blaster), cost me only 300€, but no LineageOS, CalyxOS or /e/ OS support unlike the older X3 Pro because it was not as popular among the enthusiasts.
Second-hand market is also very situational, eg in my country Pixel phones are not popular and thus the second-hand market is filled with mostly Samsung and some iPhones.