There are a people who suggest that Yosef and his brothers were accompanied by a large group of Egyptions. These Egyptians were the "official delegation" who were accompanying Yosef. Reading the description, we see that this is more like a military operation and as such would not be allowed to actually enter another country. Yosef and his brothers on the other hand continued on to Chevron to put Yaakov in Mearas hamachpelah. As a result, they stopped at the place where the Egyptians broke off and mourned Yaakov there before the continuation.
Professor Yoel Elitzur cites his father, Professor Yehuda Elitzur, in Parashat Vayechi: Goren Ha-atad with a similar answer, but states that the Egyptian military delegation had another purpose.
We read here that the delegation of mourners for Jacob consisted of
chariots and horsemen, “a very large troop.” The scope of this journey
seems to more closely resemble that of a military operation than that
of a mourners’ procession. If we analyze the verses carefully, we will
see that the delegation was actually comprised of two separate groups.
One group consisted of Jacob’s family: “Joseph’s household, his
brothers and his father’s household.” The second group consisted of
“the officials of Pharaoh, the senior members of his court and all of
Egypt’s dignitaries,” and with them, chariots and horsemen – a very
large troop. In other words, it is a small group of Israelites
traveling alongside a large Egyptian delegation. A close reading of
the verses demonstrates that, following the mourning ceremony in Goren
Ha-atad, Jacob’s sons alone proceeded on to bury their father: “His
sons did for him as he had instructed them. His sons carried him to
the land of Canaan, and buried him in the cave of the field of
Machpelah, the field near Mamre, which Abraham had bought” (50:12-13).
What perhaps seemed like a joint procession of Egyptians and
Israelites was actually two separate delegations traveling alongside
each other for the first leg of the journey. The Torah lingers on the
actions of Jacob’s sons, as well as on the large portion of the
journey that was dedicated to mourning for Jacob. However, it seems
very likely that the Egyptian delegation that set out to bury Jacob
actually had an ulterior motive for its journey. While they certainly
had great respect for Jacob – they “bewailed him seventy days” (50:3)
and embalmed him as they would their most respected figures – the
journey seems to have had a different purpose as well.
According to Egyptian sources, Egypt ruled over the land of Canaan
during that period. To maintain their hold on the land, the Egyptians
would set up garrisons in various locations. The most important of
these garrisons were located in Beit She’an and Gaza, and each year
the soldiers manning these garrisons would be replaced with fresh
troops. Apparently, this yearly changing of the guard would be
accompanied by a large military delegation.
Professor Elitzur thus concludes:
To summarize, our parasha describes a large-scale Egyptian military
expedition, a yearly operation that involved numerous chariots and
horsemen. The purpose of this expedition was to replace the troops
manning the Egyptian garrisons throughout Canaan with fresh soldiers
from Egypt.
Before each group of soldiers went off to their respective garrisons,
the delegation stopped at a central location – Goren Ha-atad – for
seven days, to mourn the loss of Jacob, the father of the
second-in-command of Egypt. After this ceremony, the Egyptian troops
all traveled to their designated garrisons, and Jacob’s twelve sons
departed for Hebron to bury their father.
