Hard to believe, but after being chosen to be “His people”, how many times did they (as a people) abandon Him, defy Him, ignore Him, turn against Him, renounce Him? It is no different today. That is why only a remnant of His people will be saved. God will keep His promise to the Jews, even though they don't deserve it.
Mathew 7:13”Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. 14But small is the gate and narrow the road that leads to life, and only a few find it.