Another interpretation: "for it was near" (Exodus 13:17). The Canaanites had only recently inherited the land, as it is said, "and in the fourth generation they shall return here" (Genesis 15:16) [and they had not yet had a fourth generation, so their measure of guilt was not yet full].
The Near Road and the Canaanites' Fourth Generation
Yalkut Shimoni on Torah 226:8
דָּבָר אַחֵר, כִּי קָרוֹב הוּא, בְּקֵרוּב יָרְשׁוּ כְּנַעֲנִים אֶת הָאָרֶץ, שֶׁנֶּאֱמַר (שם טו, טז) "וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה" [וַעֲדַיִן לֹא הָיָה לָהֶם דוֹר רְבִיעִי].