Because in many ways it seemed like an obvious way for the Democrats to avoid responsibility for Hillary's terrible 2016 campaign and it's been all hype for two years.
Once you dive a little deeper, you see some undeniable pieces of evidence in this investigation.
-Lies regarding contact with Russians, Russian Deals, sanctions, meetings, and timelines
-Putin on the international stage said he wanted Trump to win
-Indictment for hackings by name
-Russian money flooding right wing outlets
-Republican James Comey instructed by Trump to pledge loyalty and to stop investigation into Flynn.
-Guiliani openly stating his best defense against impeachment is to win the court of public opinion. Aka, smear the investigation and obfuscate the facts to the point where Congress has plausible deniability to look the other way and downplay the investigation results.
The question things seem to come down to is, did the Trump organization, the campaign, or Trump explicitly promise a reduction on sanctions so as to make it easier for Putin and his oligarchs launder money, secure financing for Trump Tower Moscow (then to give a gift of $50 million dollar penthouse to Putin), and to further other business deals. And did the Trump organization openly solicit the hacking of DNC emails to make this happen?
Wanting to lift sanctions is an acceptable policy position. Wanting them lifted so you can please your business associates, gift real estate to foreign leaders, and to secure a business loan for personal gain is a serious conflict of interest. And encouraging hacking to help win an election is problematic.
Hillary's loss made people salty. But the dirty underbelly that is Trump's business dealings is a major conflict of interest.