Why should team members participate in making a Work Breakdown Structure?
What incentive is there for the team to go through the task of creating a WBS? It looks like a lot of work and some of them won't see why it needs their involvement.
An important motive for creating Work Breakdown Structures is giving the team members responsible for doing the work some confidence that management understands the true scope of that work. Who wants to commit to a project timeline only to find out later that the work was misunderstood and grossly underestimated? The WBS can actually be used as a crucial component of protecting team morale. There is nothing worse for team members starting a project than the sinking feeling that once again their management does not understand the work at the team members' level. Once again, management will set incorrect expectations based on a coarse and insufficient understanding of what actually has to get done at the team members' desks and benches. Once again, management will ask them to do the impossible. And once again, there will be pressure, acrimony, and disappointment when the impossible is not accomplished.
Good team morale is a large lever on project success. Pay attention to morale by ensuring a thorough work breakdown is done. Then and only then do you know that the scope of the project is well understood by everyone—especially those cracking the whip to get it done within a certain time period and budget.
That brings us to the last part of the question—team member involvement in creating the WBS. The goal is to avoid unfounded expectations by management and protect team morale (and commitment to the plan!) through a schedule that is actually possible. The only way to get a feasible schedule is to make sure the team members identified all the work they know needs to be done—which is the purpose of the WBS.