Why are there limitations for length of scientific papers?
It is considered to be positive if you can express yourself briefly and make your message clear and concise. Size limits for papers are therefore partially determined by its quality of content meaning that you can communicate the substance succinctly to the readers.
There is, however, also an important economic aspect. Most journals have limitations for lengths and one of the reasons is that all papers go to copy-editing, which costs money. Copy-editing will correct linguistic errors and it is often a burden for the journals to cover these charges. A short article will therefore cost less to produce than longer articles and especially tables and figures may be costly in graphical work and typesetting.
Costs for printing and publication and distribution are obviously higher for journals in print than for an exclusive internet journal. However, the internet journal will still have costs for copy-editing and graphical lay-out of the published articles. Therefore, all journals have a page-budget which they must comply with. Therefore, most journals will have some kind of page limitations for their published articles. The journals that may allow longer manuscripts are typically open access journals where the cost of publication is put directly on the authors, but there are of course also exceptions to this general rule.