That’s because a US Permanent Resident enjoys several privileges as compared to other immigrants.
Privileges of becoming a US permanent resident--Once an immigrant become a permanent resident of the US, he gets a legal right to work and live in the US apart from getting several other benefits including financial support for pursuing higher education in the US and getting qualified for social welfare programs.
A lawful permanent resident(LPR) of the US can look forward to gaining US citizenship. The only thing worth considerable is that after becoming a US permanent resident, he must intend to stay in the US permanently or may risk losing his US Permanent Residence status.
Loosing US permanent resident status—Any foreigner or immigrant can put to risk his status of being a permanent resident of the US in any of the following cases—
• Staying out of the US for a period exceeding six months—Any immigrant who has become a permanent resident of the US can be denied of his LPR status if he remains absent from the US for a period exceeding six months or 180 days.
• Remaining out of the US for one year or longer-US Permanent Residents who remains out of the US for as long as one year or even longer period will find it hard to regain his US permanent resident status. He might be detained by the US ICE(US Immigration and Customs Enforcement) or given a conditional release or even be referred to any US immigration Court for a final decision regarding admission or abandonment of US permanent resident status.
In case, the Immigration Court finds that the concerned individual is guilty of abandoning his LPR, then he may be required to apply fresh seeking defense against his imminent removal from the US or file a new application for LPR.
Avoiding unintentional abandonment of US permanent resident status—
• Avoid long absence from the US—Foreigners must avoid staying away from the US for a period exceeding six months for any reasons whatsoever.
• Don’t sign Form I 407—Don’t ever sign a FormI-407 since it means a foreigner has abandoned his US permanent resident status.
• Maintain relationship with the US—Maintain relations with the US in any form including having family connections, property ownership, bank accounts, tax filings, employment, membership in organizations or business ties in the US.
• Re-entry permit application—Application for a re-entry permit although does not guarantee preservation of LPR status or allow re-entry into the US after a long absence. But, it does prove that the concerned LPR had the intention to return back to the US.