A missle can sit on a shelf for years, pop in fresh batteries and it is good to go.
A tank requires frequent maintenance and lots of expensive crew training to be effective.
The key element in these tank kills is lack of support. Russia has long been thought to be behind on modern doctrine and the performance to date in Ukraine drives this home: in an environment that demands high levels of force coordination and expensive gadgets, a cannon fodder offensive creates extremely high attrition, and the demographics and economy of Russia today aren't as favorable to absorbing this as in the past(older, fewer young men to lose, dependencies on the rest of the world to rearm).
Javelin: $250K missile + $250K launcher
T-72: $1000K-1200K (1-1.2 million)
Of course, non-US options are much cheaper:
NLAW: $40K
Stuhna-P: $20K
[0] https://www.armyrecognition.com/ukraine_-_russia_invasion_co...
Launcher: 250k
Getting to engage the Russkies via proxy while maintaining moral high ground and zero American casualties: priceless
That's fine as long as you don't forget that a tank is designed to do the same thing. Nobody builds a $6 million tank to destroy $3 million worth of targets.