Okay… So… This can happen depending on how you ran the composer command when you originally installed it the extension - As you can “lock in” version that you want to install. You may need to specify what version you want to upgrade to when running your composer command.
According to the Amasty Documentation under “Extension Update via Composer” you need to specify a version number. Here’s an extract:
Where x corresponds to the first version number. For example, to update the Improved Layered Navigation Extension for M2 from the 1.x.x version to the 2.x.x version you need to execute the command:
composer require amasty/shopby ^2.0.0 --update-with-dependencies
So, I guess you might need to run:
composer require amasty/module-seo-toolkit ^1.14.1 --update-with-dependencies
1.14.1 is their latest version according to their website)
Have a read through that document first.