All magic items have a very low level of intelligence. To control a magic item, you need to meet one of these criteria:
1) Have it attuned to you at the time it is first sold,
2) Have it re-tuned to you, which costs money and a month of time (normally represented in the cost of buying used magic items - which actually cost less than new magic items because they are used, but that savings is eliminated by the cost of re-tuning),
3) Be an active member of the group that defeats the prior owner and "wins" the magic item over.
Hence, when a player dies, his items were not won over by the new player or party, and go inert. You can pay to re-tune them, and wait a month, but odds are you will prefer to just buy new items and have them tuned to you right away, and the party will sell the old items for 1/2 their value (causing the new owners to spend time an resources to get them refreshed to the point where they can be resold in a month).