It's not illegal for Americans to boycott Israel. Only government institutions.
https://en.wikipedia.org/wiki/Boycotts_of_Israel
In the United States, the Export Administration Act discourages, and in some circumstances, prohibits U.S. companies and individuals from furthering or supporting the boycott of Israel. The Department of Commerce's Bureau of Industry and Security (BIS) is responsible for penalties are imposed for each "knowing" violation with fines of up to $50,000 or five times the value of the exports involved, whichever is greater, and imprisonment of up to five years.
During the mid-1970s the United States adopted two laws that seek to counteract the participation of U.S. citizens in other nation's economic boycotts or embargoes. These "antiboycott" laws are the 1977 amendments to the Export Administration Act (EAA) and the Ribicoff Amendment to the Tax Reform Act of 1976 (TRA). While these laws share a common purpose, there are distinctions in their administration.
The antiboycott laws were adopted to encourage, and in specified cases, require U.S. firms to refuse to participate in foreign boycotts that the United States does not sanction. They have the effect of preventing U.S. firms from being used to implement foreign policies of other nations which run counter to U.S. policy.
The Arab League boycott of Israel is the principal foreign economic boycott that U.S. companies must be concerned with today. The antiboycott laws, however, apply to all boycotts imposed by foreign countries that are unsanctioned by the United States.
The antiboycott provisions of the Export Administration Regulations (EAR) apply to the activities of U.S. persons in the interstate or foreign commerce of the United States. The term "U.S. person" includes all individuals, corporations and unincorporated associations resident in the United States, including the permanent domestic affiliates of foreign concerns. U.S. persons also include U.S. citizens abroad (except when they reside abroad and are employed by non-U.S. persons) and the controlled in fact affiliates of domestic concerns. The test for "controlled in fact" is the ability to establish the general policies or to control the day-to-day operations of the foreign affiliate.[135]
The scope of the EAR, as defined by Section 8 of the EAA, is limited to actions taken with intent to comply with, further, or support an unsanctioned foreign boycott.
Why? Because of the Palestinians or the territories Israel won after being attacked multiple times by it's neighbors?
Evidence of cia involvement. Should we boycott ourselves?