Adding thousands of pages at once usually spreads your existing crawl capacity thinner rather than triggering a proportional surge in crawling, so discovery and indexing of the new batch tends to be slow and uneven, and on a young or low-authority site it can crawl through painfully. The intuition that more pages get crawled faster has it backwards. Google does not hand you a bigger crawl allocation the moment you publish more; it works through the larger pile with roughly the capacity it was already willing to give your site, which means each page now waits in a longer line. This is observed behavior, and you can watch it play out in coverage reports after a bulk publish.
The mechanism is straightforward once you see the budget as fixed in the short term. If Google was crawling, say, a few hundred URLs a day across your site and you suddenly add several thousand, those new URLs compete with each other and with your existing pages for the same daily attention. The batch gets discovered in waves, with some pages indexed quickly and many others sitting in discovered-but-not-yet-crawled or crawled-but-not-indexed limbo for a while. The result is uneven, not the fast bulk ingestion people expect.
Site age and authority sharpen the effect. A young or low-authority site has a smaller crawl allocation to begin with, so a thousands-strong batch overwhelms it more severely and clears more slowly than it would on an established site that has earned a generous crawl rate. The same dump of pages can be absorbed in days on a strong domain and drag on for weeks on a new one.
There is a further risk that runs the wrong way entirely. If the new pages are thin, templated, or low-value, a flood of them can actually depress Google’s interest in crawling your site, because the crawler learns that visiting yields little of worth. Instead of more crawling, a low-quality bulk add can earn you less, as the system deprioritizes a site that suddenly looks padded.
So when you have a large batch to publish, stagger it into smaller waves rather than dumping it all at once, make sure each page is genuinely valuable, and link the new pages well so the crawler has clear paths to them. Treat the addition as something to feed in deliberately, because the crawl capacity to absorb it does not arrive just because the pages did.