I never understood what is there to be scared about.

People buy Microsoft Word knowing they won't be able to change it, because it's closed source. However it sells well.

Do people use LibreOffice because it's Mozilla licensed and not GPL? Do all those people that don't dream about modifying Word really want to add secret proprietary features to LibreOffice?

Similarly, Oracle (the database) vs MariaDB (GPL) vs PostgreSQL (its own license, basically MIT / BSD.) There are definitely people that patch databases but I wonder how many people here decided to use one and not the other because they thought "what happens if I ever want to add something to MariaDB and nobody else must get it?"

No, where is scares them is at the copyleft level, when they are writing software. You're quite right that it probably doesn't scare many when they are just using it as an appliance (e.g., a database).

Elasticsearch moving to GPL/AGPL/etc would not have blocked Amazon since Amazon already freely releases the sources of their contributions. That is why Elastic instead chose the niche license SSPL.