Why are the Jews called God's chosen people? Since all mankind descends from Adam (and later Noah), why do Jews get special designation among all other peoples, especially since they worshipped false gods and disobeyed God's word?
The Bible declares that the descendants of Abraham, Isaac and Jacob are God's chosen people, a possession for Himself called to be the "wife" of Jehovah. Nevertheless, as you say the Jewish people are not inherently better people than the rest of mankind, nor did Israel earn (much less deserve) their special status with God. In fact, God declared that Israel was a nation of unremarkable people:
The Bible says the Lord selected Israel to be His chosen people despite their lowly and unremarkable status. It was the Lord Himself Who created the Jewish people by way of a promise He delivered to Abraham, Isaac and Jacob. The Lord promised to grant these men inumerable descendants, who would inherit a special place in God's Kingdom.
The Lord's decision to award Israel a special place in His plan was simply an act of grace, not one based on Israel's merit. In other words, Israel wasn't chosen because they were special; Israel is called special because God chose them.
The Bible also says the nation has received great honor and significant advantages as a result of being chosen by God:
Among other advantages, Israel was given the word of God (to guard and deliver to the world), the covenants of promise, the Law and the tabernacle service. Most importantly, Israel was chosen to bring forth the promised Messiah. The Lord elected Israel for the privilege of receiving these blessings, and by His choosing, the Lord made Israel special and set them above all other nations on Earth.
The Lord did this out of love for Israel and out of a desire to use Israel to glorify Himself and bless the entire world. As the Lord decalred to Abraham:
Israel didn't deserve the Lord's mercy (and neither do we), but still the Lord chose to make Israel special according to His word. He did this despite their history of sin. As you mentioned, the people of Israel have been (and continue to be) disobedient to God and in violation of His word. Still, the Lord remains faithful to Israel, as Paul says:
The Bible teaches that the Lord responded to Israel's disobedience with a temporary judgment. The Lord set Israel aside for a time, while extending His grace to Gentiles in their place. Paul teaches in Romans 11 that this "switch" is only temporary in God's plan. Eventually, the Lord's attention will return to His chosen people, and in that future day He will extend His grace to the Jewish nation again. As Paul says in Romans 11, in a day to come day all Israel (i.e., those who are Israel on that future day) will be saved, because the gifts and calling of God are irrevocable:
You can learn more about the importance of Israel in God's plan by listening to our Romans study online.