I'm not sure what the strategy is right now, but there are several possible tactics at play:
Voting on the limited scope articles is very specific - the public won't be able to follow too broad a scope, and the facts here are very clear. Investigations are ongoing, so whatever comes about in those will be added to the case.
The president and his staff have obstructed Congress and Justice. The DOJ is under an AG who is not faithfully executing his office, so they are sticking to the obstruction of Congress issue for now.
Many of us have been critical of Pelosi for delaying this for so long. We are now faced with a president who will appeal everything to the SCOTUS, delaying the process. The problem with waiting for the courts on everything is that POTUS is breaking the law right now, in real time.
Democrats don't have to forward articles of impeachment to the Senate. They can vote to impeach, and not refer it to the Senate. There are no rules around the timing of this, either. They could continue to add to the articles of impeachment. They could decide to censure the president instead.
Regardless, the GOP has gone all-in for Drumpf. Wagon's hitched, and as more and more of the truth comes out, it is not going to get any better for Repubicans. If you think any documents, recordings or fact witnesses under oath are going to exculpate him on this, you are a fool.
Nobody really knows how this is going to shake out. Sounds like there are a handful of Repubicans who are fine kicking him out of office, they just can't break ranks publicly. If you use the analogy of playoff sports, "That's why you play the game."