Why Jacob left
After Jacob obtained the blessing Isaac had intended for Esau, Esau planned to kill him. Rebekah urged Jacob to flee to her brother Laban in Haran, and Isaac sent him away to take a wife from Laban’s daughters. Jacob went out from Beersheba toward Haran and dreamed at Bethel on the way.
“Left home” in common search language usually means this departure from Canaan to Padan-aram, not a later move within the land.
How about 77 is reached
Joseph was born after fourteen years of service, when Jacob was about 91. Those fourteen years began when Jacob arrived at Laban’s house. Arrival and first meeting with Rachel therefore fall near age 77, which is also the approximate age when he left home.
Some popular timelines print other figures for this period. BibleAV prefers the reconstruction tied to Joseph’s fixed ages and Jacob’s age of 130 in Egypt, and marks intermediate years as approximate.