The reason why the Trump investigations are taking so long, is that in investigating Trump, so many crimes are beign discovered, done by the people all around Trump, that it has slowed down the direct investigations for Trump himself. That is why it is taking so long.
It takes 3 years or more to settle a simple "slip & fall" lawsuit.......5+ years if there is actual injury! Why you think this, with all its' ramifications, will happen "now" I do not understand!
Thorough investigation take time. I've worked investigation that took 4, 5, 6 years. There's lot's of evidence and discovery to go through. TV and movies give a false impressions of how long some investigations can take. The Watergate investigation took more than 2 years.