I guess to me, it comes down to time and cost. Generally, although things change all the time, if you can get 60% support in the House, it means that you've got at least some bipartisan support. Then, you know if it's worth it to go through all of the divisive steps to sign off on the Inquiry and send the Articles to the Senate.
In this case, they had essentially zero support from the G.O.P. in the House. And the chance of the Senate supporting the measure to a 2/3 majority was as close to Absolute Zero as is possible. Even if I agreed with the democrats on this issue, I wouldn't have wanted to spend the time and money on it. And that's especially true if you believe the left leadership that Trump is bound to do something sinister......if that is the case, and it's truly something tyrannical, illegal, bad for the country, etc., then you could just wait for that and impeach then, because you'd really have an issue that would garner bipartisan support.