The only practical argument in favor of this approach is “we won’t be able to replace Obamacare until Obama is out of office, until then, we will maintain the subsidies because simply too many people will be crushed economically by this bad law if we don’t.”
The counter-argument is as described above - the more these subsidies get entrenched, the less likely they’re ever going away.
These subsidies are not going away. Obamacare is not going away. It is too useful for the politicians, no matter their labels. Each election from now on will be fought out on which candidate can tweak the system more favorably for his key constituencies. That is what happened in England.