Actually, it’s a requirement of the Wi-Fi Specification and Wi-Fi Standards that anything capable of connecting via WPS also supports the passphrase method of WPA2-PSK. Clients can support the Passphrase method but opt-out of WPS if the manufacturer so wishes, but not the other way round.
Likewise, supporting WPS at all is completely optional - manufacturers of both AP and Client can opt to not include WPS at all if they don’t want to support it.
Strictly speaking, your Ecodan is non-compliant with the spec and therefore isn’t Wi-Fi Certified.
The fix is easy - just add the missing functionality in future firmware updates.