If they did it would significantly affect their business operations. The volume of chips they'd have to replace, Haswell, Broadwell, Skylake, Kaby Lake and Coffee Lake architectures. We're talking probably Billions of processors just with those chips from the last 3-4 years. I don't expect they would replace any older than those.
The cost to them wouldn't be so much the cost of manufacturing those processors but the time they would lose manufacturing that kind of volume to satiate the demand for replacements when they're still launching new processors that they actually want to sell. You guys I don't think follow the market closely but the Coffee Lake CPU's which just launched in October 2017 have been very hard to get a hold of for the past two months, not due to high demand but due to very few processors in the market. Some retailers said they only received 10 pieces total for their entire organisations over a 30 day period from the October launch.
Intel has been pushing up the launches of their processors to fight AMD's Ryzen chips (which are not as badly affected by these bugs coincidentally). Intel planned to launch Coffee Lake in February 2018 alongside a new chipset called Z390. But because AMD's processors (1800X, 1700X, 1700, 1600 etc) have been eating into Intels marketshare quite rapidly they decided to push Coffee Lake up and Z390 wasn't ready in time so they rebadged the Z270 chipset as Z370 and launched it with the new processors.
The whole thing has really left egg on Intels face as they knew about these bugs in June but due to the threat presented by AMD they decided to launch Coffee Lake with known speculative execution errata in October. This making the whole situation for themselves even worse than it was already.
Personally I'm not a fan of these companies they all do despicable things to different degrees but Intels maliciousness and incompetence combined with them knowingly shipping defective product is really disgusting. I hope that they get some big repercussions, being forced to issue replacement chips for anyone that wants one would be a good start.