mRNA vaccines have been undergoing active research for decades, and in particular the lipid nanoparticle delivery mechanism used in both the Pfizer and Moderna vaccines was first used in 2018 in a (non-vaccine) drug called Onpattro[2]. Without this technology, Moderna in particular was having issues with excessive side effects as late as 2017[1].
As such, the Covid-19 vaccines from Pfizer/BioNTech and Moderna could not have been developed pre-2018, and - absent a deadly pandemic that requires taking extreme measures (such as using very large trial groups) to hasten the timeline - normally vaccines undergo development over a period of many years[3] to collect sufficient data to ensure effectiveness and to ensure that the long-term side effects are well understood. Moderna in particular was, prior to the Covid-19 pandemic, working on developing vaccines to target cancer using mRNA technology[4]. Had the pandemic not occurred, one would therefore not expect to have seen any approved therapies until the mid-to-late 2020s at the earliest (and probably later, given how often vaccines and other drugs fail in human trials).
In short, the issue was not that pharmaceutical companies were disregarding the technology, so much as simply the last remaining breakthrough needed to be made - and now that mRNA vaccines have proven themselves to be safe and effective, there'll be no shortage of effort to apply them to new diseases.
[1] - https://www.statnews.com/2017/01/10/moderna-trouble-mrna/
[2] - https://www.statnews.com/2020/12/01/how-nanotechnology-helps...
[3] - https://www.historyofvaccines.org/content/articles/vaccine-d...
[4] - https://www.statnews.com/2017/01/10/moderna-trouble-mrna/