וְלֹא־נָשָׂ֥א אֹתָ֛ם הָאָ֖רֶץ לָשֶׁ֣בֶת יַחְדָּ֑ו כִּֽי־הָיָ֤ה רְכוּשָׁם֙ רָ֔ב וְלֹ֥א יָֽכְל֖וּ לָשֶׁ֥בֶת יַחְדָּֽו׃
И земля не могла их вынести, чтобы они могли жить вместе; ибо их содержание было велико, так что они не могли жить вместе.
Rashi
ולא נשא אתם AND THE LAND WAS NOT ABLE TO BEAR THEM — It could not provide sufficient pasture for their cattle. The phrase is elliptical and a word must be supplied, for instance: the pasturage (מרעה) of the land was not able to bear them — for this reason the word נשא (masculine) is used (to agree in gender with מרעה; the suggestion is that נשא cannot have הארץ as subject since that noun is feminine).
Chizkuni
ולא נשא אותם, “the land did not offer sufficient virgin land to support their combined flocks and herds.” The Bible using the term ארץ, as if it were masculine here, is not a unique example. It also occurs in the masculine mode in Zachariah 14,10, as well as in Isaiah 9,18, and in Isaiah 33,9.
Sforno
ולא נשא אותם הארץ, the grazing land available in that region was inadequate for their combined herds.