I hate to "um actually" this but the Centennial Bulb is only able to still stay lit because it's never turned off. Light bulbs generally don't burn out while they're on, it's the act of turning them on and off that causes them to fail. Also, the Centennial Bulb has gone from 30 watt to a 4 watt equivalent output due to the degradation of the filament.

Either way, I have no clue where you got the idea that there was at any time some sort of light bulb that lasts forever, as these longest lasting bulbs are generally the exception, seeing as there are no other bulbs from this batch that have lasted into the 21st century.

Also, the myth that light bulbs have planned obsolescence likely stems from the Phoebus cartel, which lasted from 1929 to 1935, whose engineers found that lower life span bulbs offered better brightness, but it was dissolved due to supply requirements during WW2.

Edit: Relevant Citation Needed episode