End of security support will affect online stores running version 1 financially because it may stop them from accepting online payments.
By switching to Magento 2 , the problem can be avoided, but the upgrade is difficult and costly.
The main issue will be security. Payment gateways connected to legacy Magento 1 stores will almost certainly be shut down by financial institutions in future, as they realize the risks of an end-of-life commerce platform connecting to their systems
This will cause old M1 stores to be cut off from receiving payments and leave store owners with EFT payments as their only viable option.
Read more about it here: Magento Development UK