You do get some twits on TV. Flu has not been eradicated.
The reason why incidence of flu appears to have plummeted is simply that the health services are no longer testing for the flu virus, all resources being diverted to testing for SARS-CoV-2.
Lockdowns do have an effect, and the incidence of flu will have dropped in lock-down countries, just like COVID-19. In countries which are not under lockdowns, and there are plenty of those, the flu virus will also be less prevalent, because a proportion of the population will also be shielding.
It's perfectly possible tor the same person to be infected with multiple viruses. Anyone with COVID-19 could also have the flu, or another type of the coronavirus, e.g. the common cold. But once you're tested for SARS-CoV-2, the medics won't test for anything else.
Another reason for the apparent "disappearance" of flu cases, is that people are at last taking sensible precautions, e.g. washing their hands, and taking plenty of Vitamin D, Vitamin C and Zinc, to keep their own immunity at it's highest potential.
There is an issue with the sensitivity of the SARS-Cov-2 PCR tests, it identifies the presence of even the lowest numbers of the virus captured on the nose swab, because the sample is then grown multiple times in the lab, doubling each cycle, as many as 35 cycles, (e.g. 2x2x2... 35 times, which is a very high number.) In a nose swab, these viruses could have come from your chest (if you have been infected by the coronavirus), or you could have just breathed it in earlier that day, but they haven't infected you yet. In fact, they might not infect you at all, depending on the strength of your immunity and how many viruses you have breathed in (a.k.a. viral load). But the PCR test doesn't know whether the viruses came from your chest or the ambient. If you're in the same household as someone who has become infected, you're very likely to have SARS-COV-2 on your nose swab, but it's by no means certain that you will become infected. But if the test detects these traces, then you will be deemed positive, whether you are infected or not.
So, even if you have the COVID-like symptoms and you test positive, it could be that you have the flu and not COVID-19. The health services simply don't test for all respiratory viruses. This isn't so good for identifying which flu strains are likely to be prevalent next year, so they might well inoculate us against the wrong flu strains next year.
Another thing that most people aren't aware of, is that after you've become infected by SARS-CoV-2 and then go on to develop the symptoms, by day 7 to 10, your immune system has killed off all the SARS-COV-2 viruses, and there are no live viruses left in your body. Instead, the body is full of viral debris, lots of dismembered particles of the virus, which also give a positive test result, even though you're no longer breathing out live viruses. Most people go on to recover quickly, but will be testing positive for weeks to come. Some will get very sick, some will end up in ICU and on ventilators and some will die. What most people don't realise is that they will be seriously ill and die not because of the viruses (which are dead by that stage), but because of the very strong immune reaction of our own bodies. Cytokine storm, for example, is caused by our own immune system, over-reacting to the virus and it's debris in our bodies. It's that which kills.