What

are

possible

advantages

to

having so

many

different groups participate in

the

lawmaking process

A big amount of people and groups participating the the lawmaking process might slow it down, but it also makes it more reliable.

The advantage is that it is less likely that a law will be bad in some sense: it's checked by many people and this will make it more likely that any possible mistakes or undesired consequences will be "caught out".

So it ensures a good quality of the laws.