What's so bad about using a phone that no longer has official support?

My Pixel 5A with GrapheneOS is working funky for unrelated reasons, so I temporarily revived my old Pixel 1 which has DivestOS installed on it. Even on the DivestOS website, there is a warning about the Pixel 1 that states that device is end of life by the vendor. So exactly what type of risk am I facing by using this old phone that has no official support but still gets updates by the DivestOS team? (Also secondary question, why …

bad phone privacy support