For most practical purposes (like knowing when to show up at a meeting), you need to know local time.
Even if you got rid of leap seconds, you still wouldn't know for sure how many seconds there are between now and some date and time in 2022 because you don't know what the local timezone will do. It's not clear why this is a useful calculation? For scheduling events in the future, you need to store the timezone (or location) and local time anyway.
Unix time is a useful approximation for comparing and converting between local times.
Even if you got rid of leap seconds, you still wouldn't know for sure how many seconds there are between now and some date and time in 2022 because you don't know what the local timezone will do. It's not clear why this is a useful calculation? For scheduling events in the future, you need to store the timezone (or location) and local time anyway.
Unix time is a useful approximation for comparing and converting between local times.