Bulbs have a certain life. If you change them all at the same time then it's reasonable to expect them to die more or less at the same time. Obviously it won't be 100% exactly the same time but within a window.
The other issue is bulbs age and change colour. If you're printing colour then having a mix of old/new bulbs might cause problems.
I'm guessing this is a new to you enlarger? The bulbs could have gotten jostled in the move. They may just be old. When I got my smaller Durst the bulbs died not long after it got home. The replacement bulbs have lasted since then.