Why do we have different electoral systems?

Why do we sometimes have top down and other times bottom up elections? Examples:

• Top down: During presidential elections people vote for the president and the parliament. After the election, the president appoints people to top jobs.
• Bottom up: During worker's union elections workers vote for their representatives. The representatives vote for the union president (bottom up).

Do these election types have any logic depending on their context or are they a result of historical accidents?