The reason for them being treated differently is, of course, is because they are not Israeli citizens. They can vote for their own PA government, and once upon a time they did. Given that Arab citizens of Israel do have equal rights under the law (although they do suffer from discrimination, as minorities in every nation do) calling Israel an apartheid state for not allowing non-citizens to vote is absurd.
However, there are millions of full citizens of the United States who are not allowed, by law, to vote in national elections.
Residents of Puerto Rico, the US Virgin Islands, Guam and other territories cannot vote in federal elections. The US Constitution requires a voter to be resident in one of the 50 states, or in the District of Columbia, to vote in federal elections.
That's about 4.2 million US citizens who are disenfranchised - by law - from voting for their president.
But that is only one group of US citizens who are not allowed to vote. Another group is even larger.
About six million people who committed crimes cannot vote in US. In some states, even after prisoners are released they do not regain voting rights.
Not only that, but about three quarters of the US citizens who are denied the right to vote in federal elections are minorities - about 60% of prisoners and nearly all of the residents of the US territories, - which is even further indication of US apartheid based on race!
Obviously, to call the US an apartheid state is absurd. But anyone who claims that Israel is an "apartheid state" must believe that the United States is far more guilty of the crime of apartheid than Israel is, given its legal discrimination against about 10 million US citizens.
For some reason, none of the Israel haters, who pretend to care so much about equal rights, are bothered by US legal discrimination against far more people who are actual US citizens. Isn't that a shocker.
(Note: In Israel, prisoners can vote for Knesset and arrangements are made for them to do so.)