Why do budgies........?

Actually, budgies can live over 10 years, if they're healthy. Those ones may have been sick, or maybe your friend or someone in his/her family inadvertently did something that was bad for them, like using air fresheners or chemicals or stuff like that around them, or cooking with Teflon-coated things (though I'd think that would've killed them both at the same time), or maybe they ate something toxic, like avocado. There's no way to really make any kind of guess without knowing how they were cared for or what went on in the house while they were there, and even then, a necropsy may be the only way to know for sure.

They don't have short life spans. They can live up to 10-15 years. l have my budgie for 1 year(she got sick and died) my friend got a budgie 4 years ago and she still has it!