SETI was always based on very long odds, as well as being poorly funded because of dismissals like those in some of the comments here. The main signal listening is done in a narrow band that has least attenuation by hydrogen atoms and dust, on the assumption interstellar signals would be sent there. The uncertainties are very high. It has been more about reasoning our way through what we might expect, than really realistically looking.
The paradox is really that, given the size even of just our galaxy, the gigantic number of stars, we would expect some clues. Techno-signals could include laser or radio noise or other light or gamma ray bursts, nuclear or antimatter explosions, space mirrors and star-occlusion not linked to an appropriate planetary mass, unstable elements in atmospheres. Our expectations of numbers are arranged into the Drake Equation, and in general recent observations have increased the already high expected numbers of civilisations it outputs.
Life started earlier than previously thought on Earth. Only a few hundred million years after the end of cosmic bombardment, suggesting that with physical characteristics of our planet (goldilocks zone, rocky with molten iron core, plenty of water) life is quite likely to occur. And happened over a very short time compared to the age of the universe. Whether life occured on Mars or Europa will add information.
It has turned out most stars have planets, and that rocky planets are common, as we have got better and better at observing solar orbital wobbles and planetary transits. 99
Still looking at 'super earths' or bigger though. Some information can be gleaned about atmospheres too, and none with oxygen have turned up yet. First exoplanet with magnetic field observed 2014.
I must say I think the questions you ask are exactly the right way to go about looking at the issue. The Fermi Paradox is up there with Dark Energy and Dark Matter as one of the great outstanding mysteries. Narrowing the relevant unknowns, and focusing attention on research that will narrow them further, shouldn't be treated as fringe science, but as addressing some of the key issues of cosmology and biology.
Some success with atmospheres, in 2014 the first magnetic field inferred en.m.wikipedia.org/wiki/HD_209458_b and in 2017, super-Earth GJ 1132b https://phys.org/news/2017-04-atmosphere-super-earth.html
Breakthrough Initiative, Watch project aims to look at 'nearby' stars for biosignitures inc oxygen en.m.wikipedia.org/wiki/Breakthrough_Initiatives Antimatter makes gamma rays, hot topic for astronomers, closely watched. Very high energy bursts remain unexplained, and interstellar comms is a candidate.
Our own current level, sure [we wouldn't have observed]. But, we expect a higher level of technology to persist, for a long time, with increasingly noisy signals. For that to not happen for other occurences of life millions of times in our view, we then have to assume there is a en.m.wikipedia.org/wiki/Great_Filter, or a much better way of communicating/travel/fighting based on physics we don't know yet. Or, we are in a simulation.
Edited to add: This consideration of whether the Simulation Hypothesis is the best answer to the Fermi Paradox has some great quantitative statistical work on expectations for various scenarios of intelligent life occurence and distribution https://www.stat.berkeley.edu/~aldous/Research/Ugrad/mark_yu_haihan.pdf 99