why seatle.html is missing on subsites

Question

I am confused on how i should be editing master pages on site collection & sub sites.now i have a team site collection inside sharepoint 2013, and when i check its master pages inside SP designer i found the following, where seatle.html is missing:-

so i enable the "SharePoint Server Publishing Infrastructure" site collection feature and then i refresh the mater pages list where the seatle.html appear :-

now inside the team site i created a new subsite of type team site, then i opened the new sub-site inside SP designer . But i could not find seatle.html. and now i need to modify the master page for the sub site, so i did the following:-

1. i copy/paste the seatle.master.
2. then i define the new master page as the default and custom master page.
3. then i edit the new master page and i did the modification

now my team sub site had the modification without any problem.

but i have the following questions on the above:-

1. why the site collection will not have seatle.html unless i activate the site collection feature?

2. for the sub-site , seems there is not any way to have a seatle.html for it , so is my process of copying the seatle.master and do the modification inside the new seatle.master copy a correct approach.

3. now inside the team site collection which have the "SharePoint Server Publishing Infrastructure" feature enabled, i copy/paste the seatle.master but when edit the copy and try to save it i got the following error :-

server error: this file may not be moved,delete,renamed or otherwise edited

so why i was able to edit the seatle.master copy inside the subsite, while i could not do the same inside the site collection ?

Answer 1

The Html file is being used by Design Manager, and created as when you activate Publishing Infrastructure Feature. Html file doesn't come with team sites template.

Update after your comment:

It is something that you should decide at top level site of a new Site Collection, whether or not the publishing feature will be needed within that Site Collection because this can greatly impact the decision on which site template is the best choice for the top level site. If top site has publishing feature activated, so the subsites will inherit publishing, or else subsites based on team site template will eventually be converted to publishing with no real connection of publishing site collection as a parent. Also, master pages provisioning (.master/.html ) is decided at top site level, which largely decided if the site collection is publishing/team.