iPhone 12 Pro completely dead

Only 3 years old Jan 21 - Jan 2024. Never dropped or mistreated, always up to date IOS, screen protector and case always on, battery health was 99%, absolutely no signs of malfunction. On Jan 9, 2024 I plugged it in to charge with an official charger and cord, went back a few hours later and the screen would not respond, tried the 3 step revive, did the 1 hr charge again & NOTHING! I phoned Apple Support on my husbands iPhone XR, they step me through the same process, NOTHING. Off to the Apple store that day (12.40pm apt) to see one of the Apple Experts. They do a two step diagnostic, air out some minor fluff from the charging port but say the phone cannot be revived on the second attempt, it's dead. They point me to buy a new one or do a costly repair as it's out of warranty (of course it is, it's 3 years old). I ask what/why went wrong, they shrugged their shoulders & say they don't know what caused it to die and I was just unlucky! No trade in price given either as the phone cannot be turned on! Have not bought a new iphone, I would like to know why my perfectly fine in working order iPhone 12 Pro simply died. It's just not a good enough response from Apple instore, Adelaide, South Australia.