Perhaps it has something to do with what the writer of Hebrews states:
10) We have an altar, of which they have no right to eat who serve the tabernacle.
11) For the bodies of those beasts, whose blood is brought into the sanctuary by the high priest for sin, are burned without the camp.
12) Wherefore Jesus also, that He might sanctify the people with His Own Blood, suffered without the gate.
13) Let us go forth therefore to Him without the camp, bearing His reproach.
14) For here we have no continuing city, but we seek one to come.
15) By Him therefore let us offer the sacrifice of praise to God continually, that is, the fruit of our lips, giving thanks to His Name.
Hebrews 13:10-15
The writer of Hebrews states that Jesus suffered without the gate Hebrews 13:12, and we see in the following verse we as His followers are to bear His reproach, so that we don't seek earthly Jerusalem but the Heavenly Jerusalem; Hebrews 12:22-23. IMO this is why the Temple in Ezekiel is outside the City.
