Why can electors change their votes? Because YOUR STATE does not prohibit it. Electoral votes are for the STATES to vote for presidency. Anything translating popular vote into state vote is a STATE issue, not a federal issue.
What would happen if the electoral college were abolished? Small-population states would lose voice and large-population states would gain voice. This would be similar to abolishing the Senate and would be one step larger to a giant federal government and weaker, more homogenized state governments.
I'm not sure about you, but I personally thing the Federal government already is too large, too wasteful, and too powerful. I'd prefer it stick to constitutional basics, protection, and state-majority approved projects.
The Constitution gives the power to the state legislatures to decide how electors are chosen, and it is easier and cheaper for a state legislature to simply appoint a slate of electors than to create a legislative framework for holding elections to determine the electors.
The two situations in which legislative choice has been used since the Civil War have both been because there was not enough time or money to prepare for an election. However, legislatures can deadlock more easily than the electorate (which lead to the 1789 failure of New York to appoint any electors).
Currently, Presidential candidates on each state's ballot submit a list of qualified electors, in a number equal to senators + representatives for that state, to the Secretary of State’s Office.
The electors for whichever candidate wins the election for that state are the chosen electors who participate in the Electoral College at the State Capitol 41 days after the popular election.
For the states of Maine and Nebraska, rather than winner-takes-all for the state, each congressional district is voted separately, and the 2 extras are sent with the overall state vote. In the 18 state contests in which this method has been used, only once has it achieved a result different from winner-take-all: in Maine, in 1828, 1 of Maine's 9 electoral votes went to Andrew Jackson.
For DC, there are 3 electors, so there's only one congressional district.
Presently, the Electoral College is comprised of 538 people, one for each representative and senator for each stare + DC.
To be elected president, a candidate must receive at least 270 of the 538 electoral votes cast nationwide.
If no candidate receives 270 votes, the final decision is made by the U.S. House of Representatives. The House would vote against the top three electoral-vote receiving candidates, and the candidate receiving a majority (26) of states would become President-elect.
Only two American presidents have been chosen by the U.S. House of Representatives because they lacked enough Electoral College votes. In 1800, Thomas Jefferson and, in 1824, John Quincy Adams both took office after the election was sent to the House of Representatives.
Similarly, caucas and national conventions use "delegates". These are pledged party members who are chosen to accept votes for the party's candidates. If a candidated drops out, they may pledge their delegates to another candidate, boosing their chance of becoming the party's ticket nominee.
Electors are state and not federal functions. The Supreme Court in 1952 (Ray v. Blair, 343 U.S. 214) ruled in favor of the state's right to require electors to pledge to vote for their party's nominee, as well as to remove electors who refuse to pledge.
A faithless elector is a member of the United States Electoral College who does not cast his/her electoral vote for the person whom they have pledged to elect.
24 states have laws to punish faithless electors, though none have ever been punished. Michigan and Minnesota can change the votes of faithless electors to the required vote. The other 22 states can simply punish after the fact. Regardless, electors are censured or otherwise outcast by their parties if voting counter to pledge.
To date, faithless electors have never changed the otherwise expected outcome of the election.
There have been 158 faithless electors to date:
71 were due to death of the original candidate
2 were due to abstaining from any vode
23 were in 1836 by Virginia
The rest were errors or personal changes.
There's no legal sanction against faithless delegates, but it would pretty much destroy their ability to operate in national politics as word got out (minutes?)