Almost all CPUs these days work natively in little-endian. To operate on big-endian numbers, additional byteswap instructions are needed.
For most things, I think this effect is negligible. Network protocols need a convention to represent things, and Bitcoin's creator picked one. The actual choice barely matters.
Displayed precision ≠ Stored precision
Note that the block timestamp is stored as a 4-byte number of seconds since 1970-01-01T00:00 UTC (the Unix epoch). However Blockchain.com show this in a more human readable form rounded or truncated to the nearest minute (2011-05-21 18:26). So if you convert that human readable time back to an integer, you will get a ...