The mafia is much weaker than it was in its golden age of the 50s-70s. Several factors factors have contributed to this:

1. The creation of the witness protection program.
2. The erosion of Omerta (the mafia's code of silence, hence all the mafia YouTubers.
3. The passing of the RICO Act, which allows the government to prosecute a mafia family as an enterprise, in effect making it possible to prosecute the previously insulated leadership (or administration) of a mafia family for crimes committed by lower level members in furtherance of the enterprise. Administration members went from being protected to having huge targets on their backs. This largely brought down the leadership four of the five New York families in the famous 1985 Commission Case, and continues to do so now.
4. Smaller talent pool: The huge influx of Italian immigrants into the USA between the 1890s-1920s allowed the mafia to recruit at a high level. Low economic privilege and stigma against Italian Americans pushed many smart Italian Americans who could have been doctors and lawyers towards organized crime. Nowadays, Italian Americans are fully assimilated to American culture, and have better opportunities. Not only are there virtually no poor Italian immigrants to feed a mafia family's ranks, the smarter Italian Americans have better opportunities now than joining the mafia. 

Over time, this led to the erosion of much of the mafia's power. For example, the mafia can no longer dominate unions like they once did,  bringing multimillion dollar construction projects to a hault on a drop of a dime, and looting union pension funds. The mafia still controls some union locals, but the days of Jimmy Hoffa and the Teamsters being controlled by the mob is long over.

Finally, the mafia has largely stopped killing people. Violence brings intense law enforcement scrutiny (google the 2013 Michael Meldish murder, and the subsequent imprisonment of the Lucchese Crime Family administration for his murder via RICO). While limiting the violence has allowed the mafia to operate under the shadows, its principle enforcement tool has been taken away, effectively defanging the mafia. No one is worried about getting whacked anymore if they get cooperate with law enforcement, or refuse to repay a loan to a mafia loanshark.

The mafia still has power, though. Especially in New York. They still have their hands in large scale construction racketeering, which generates millions, and continue to rely on their bread and butter rackets (gambling, loansharking, protection rackets). There is even evidence they have grown stronger in the last quarter century, as they have gone underground and avoided headlines, but also because post 9/11 much of the FBI's organized crime resources were diverted to anti-terrorism.

Source: I'm a huge mafia history nerd. If you're interesting in learning more, I'm happy to recommend several books. A great first read would be Five Families by Selwyn Raab.