Yikes... Can you please tell me what do all of those modules do?
Depends on the modular system, really. That's part of the fun.
On mine there are three different sequencers, for example: a suite of STG Time modules that control both voltages and gates, a Q119 (Dotcom's "new" sequencer design), a Q960 (essentially a reissue of the old Moog 960). Each has different strengths and weaknesses. For example you can't control individual gate length on the Q119 (not internally at least) but it can do things like chain 24 steps without the use of an external module, operate in radom mode, etc. One doesn't need all three (and indeed there are models by companies like Moon Modular that do other things still) so it's nice to have the variety. Some people don't want or need any sequencers whatsoever though. You don't need to be constrained with a modular's feature set.
Similarly, I have several filters because they all have different characteristics. Dotcom only sells a few: a Moog-inspired ladder filter, a multimode, and a fixed filter bank. But I also have filters from other vendors: an ARP-inspired lowpass, an EMS-style lowpass, a Polymoog three-band clone, a lowpass gate, a copy of the Steiner Synthacon, and a couple of others.
Some people like lots of LFOs. Others wants many and complex envelope generators, or need plenty of VCAs to allow dynamic control over other control signals. Some chase polyphony, while others want a lot of Chowning style FM capability, or wavetable capability, or just to use the thing as a giant FX processor for their guitar. That's the joy of modulars: you chase the feature set that works for you.