To reply to your post in reversse Australian trucks being armored (approx 40% if memeory serves?) does not mean the Russian trucks are all armored so careful not to compare one nation to another.
Logically your logistics you would have traveling under escort however are they actually doing this?, If so is it at all times?, some times? and how heavy is the escort if present?
Is it really an expensive way to use a Javelin though? Sure use it on a tank and you knock out a multi million dollar piece of machinery compared to a truck that might be worth $100,000 but it isnt so much the direct value of the asset but the indirect you should consider. You knock out a truck and you inflict a direct reduction on their logistical capability, Knock out multiple trucks and combat capability for units supplied by them can be severly hampered if not wiped out. No need to risk a fight with a tank if you can keep that tank from being refueled and armed.
This wont apply to all nations, Some take logistics more seriously then others, others are tied back by lack of funds, stupid decisions or just institutional systems delaying or stopping improvements but in the Russian context which suffers from a logistics capacity far to small to support the assets they field every truck taken out has a larger impact in supplies delivered compared to say Australian forces. Every time Russia fires of an MLRS, That is a truck load just to refill that one volley, And Russia loves the MLRS and artillery for their forces so big logistical strain without the trucks to support them.