The Trump Administration was quick to recognize Juan Guaido as the rightful ruler of Venezuela, but going from that to the de facto ruler is taking Guaido a lot longer than he apparently expected. He’s planning a major May 1 march.
President Maduro won elections both in 2013 and 2018. Guiado did not compete in either presidential election, but claims power by virtue of being the opposition leader and insisting that the 2018 vote he didn’t compete in was invalid.
And while the US seemed to believe their endorsement would put Guaido in power, it clearly hasn’t so far. It may ultimately be that Guaido would’ve found it faster to actually run for the office of president than awarding it to himself and then trying to convince everyone else.