Why do Linux file system have a maximum file size?

As Frank Rizzo said, the maximum length of a file is determined by what data type of file pointer (32 bit or 64 bit) the filesystem supports. _LFS64_STDIO for linux means largefiles is supported by stdio. h routines – as an example. You need to read thru unistd.

What is maximum file size in Linux?

file size: On 32-bit systems, files may not exceed the size of 2 TB (241 bytes). file system size: File systems may be up to 273 bytes large.
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Table A.2. Maximum Sizes of File Systems (On-Disk Format)