but many of them are not available on familysearch, for example film no. 1311195. I don't mean that they are only available at a family history center, I mean that there is no digital version at all. Why is that?
I am not connected with FamilySearch
The Catalog record for 1311195 is https://www.familysearch.org/search/catalog/273300
The record description is "Records of births, marriages, deaths v. 3- 8(p.1-660) 1820-1933"
The most likely reason is that these records are not available for privacy reasons because there are records up to 1933, and generally birth and baptism records within the last 100 years are not released. Currently FamilySearch does not split up digitised microfilms, but that may happen in the future. In any event, you would expect these records to become available in 2033 or 2034.
It is true that all microfilms have been digitized. But not all digitized microfilms can be published due to privacy laws and lack of permission from record owners/custodians.
The film you mentioned is digitized, as indicated by the presence of a Image Group Number (DGS).
Further to Maureen's comment, there is a digital version of this film, clearly indicated in the catalog: it is digital image group 7730314.
Many people -- including some FS employees -- make the assumption that "digitized" equals "online". Trouble is, this is false. Digitized just means that there are digital files corresponding to the film somewhere on FS's computers. Whenever possible, those files are put on a public server at FS, but when there are restricted images in the files, they cannot be made public. (Usually the restrictions are privacy-related, but there can be other, contractual reasons for a restriction.) FS simplifies its life by enforcing restrictions using an all-or-nothing approach: if there is a single restricted image in a digital image group, the entire group is restricted.
Welcome to the "Community.FamilySearch" Forum, with what appears to be your first post.
I am just another 'lowly' User/Patron ...
[ And, I happen to be a Member of the Church ... ]
Just in passing ...
Further to what has already been proffered ...
Just because, "All" FHL Films, have been "Digitized", DOES NOT, mean that ALL will be available 'On-Line' ...
And, that even means, through a "Family History Centre" of the Church (or, an "Affiliate" Library) ...
Here are some "Knowledge Articles", in 'FamilySearch':
I know, that this certainly does not help/assist; but, I hope, that this may provide you with, some additional, insight; and, perspective.